Method and Apparatus for Directional Centralized Contention Based Period in a Wireless Communication System
A method of communication includes allocating a portion of a superframe centralized contention based period where the access method is based on directional ALOHA. The centralized contention based period is divided into equal time slots, and each sequential set of N time slots forms a time cycle. During a time cycle, a wireless device listens for requests from other wireless devices while it changes its receiving direction from one time slot to another.
This application is a continuation of U.S. patent application Ser. No. 12/911,732, filed Oct. 26, 2010, which claims priority under 35 U.S.C. 119(e) to U.S. Provisional Application Ser. No. 61/259,621, filed Nov. 9, 2009.
FIELDCertain aspects of the present disclosure relate to wireless communication, and particularly, to directional channel access in a wireless communication system.
BACKGROUNDIn one aspect of the related art, a wireless communication system comprises a set of devices supporting at least one of a single-carrier (SC) physical (PHY) layer and an Orthogonal Frequency Division Multiplexing (OFDM) physical layer may be used for millimeter wave communications, such as the systems envisioned in the Institute of Electrical and Electronic Engineers (IEEE) 802.11.ad and IEEE 801.15.3c standards, and the Wireless Gigabit Alliance (WGA). The PHY layer may be configured for millimeter wave communications in the spectrum of 57 to 66 gigahertz (GHz), or Ultra Wide Band (UWB) communications in the spectrum of 3.1 to 10.6 GHz.
To allow interoperability between devices or networks that support either single-carrier or OFDM PHY modes, all devices further support a common mode referred to as a control PHY. Specifically, the common mode is a single-carrier base-rate mode employed by both OFDM and single-carrier devices to facilitate co-existence and interoperability between different devices and different networks. The common mode may be employed for beaconing, control, management, and communicating command and data frames (packets).
In another aspect of the related art, devices typically employ one or more Golay codes to provide spreading of different fields of a packet. Complementary codes, first introduced by Golay in M. Golay, “Complementary Series,” IRE Transaction on Information Theory, Vol. 7, Issue 2, April 1961, are sets of complementary pairs of equally long, finite sequences of two kinds of elements. These complementary pairs have the property that the number of pairs of like elements with any given separation in one code is equal to the number of unlike elements with the same separation in the other code. The complementary codes first described by Golay were pairs of binary complementary codes with elements +1 and −1, wherein the sum of their respective aperiodic autocorrelation sequence is zero everywhere, except for the center tap.
In a wireless network, such as a wireless personal area network (WPAN) or a wireless local area network (WLAN), devices typically use a slotted ALOHA protocol or a carrier sense multiple access/collision avoidance (CSMA/CA) protocol to access the wireless medium. However, these access methods do not perform well when one or more devices use directional antenna patterns for their transmissions and/or receptions.
Therefore, there is a need in the art for a directional channel access protocol for devices that may have directional antenna systems, such as phased antenna arrays, directional antennas, or sectored antennas.
SUMMARYAspects disclosed herein may be advantageous to systems employing millimeter-wave WPANs or WLANs (such as the WLANs described by the IEEE802.11.ad, IEEE 802.11.ac and WGA protocols). However, the disclosure is not intended to be limited to such systems, as other applications may benefit from similar advantages.
According to an aspect of the disclosure, a superframe allocated by a first wireless device contains a centralized contention period and a distributed contention period. During the centralized contention period, the first device is part of any communication link between a pair of wireless devices. The distributed contention period may be used for peer-to-peer communications between wireless devices. The distributed contention period may be used for communication between the first device and at least one other wireless device.
According to another aspect of the disclosure, a superframe allocated by a first wireless device comprises a centralized contention period that is further divided into fixed equal-size time slots. The first device changes its receive antenna pattern (also referred to as its direction) from one time slot to another in a cyclic manner. Specifically, the first device uses a first receive direction in the first time slot, a second receive direction in the second time slot, and an Nth receive direction in the Nth time slot. The first device reuses its first receive direction in the (N+1)th time slot, its second receive direction in the (N+1)th time slot, its Nth receive direction in the (2N)th time slot, etc.
According to another aspect of the disclosure, a method of communication is provided for accessing the centralized contention period by one or more other wireless devices (e.g., a second wireless device) to communicate with a first wireless device (a master device) using a directional slotted ALOHA protocol. The second device may transmit a frame on a time-slot boundary using a transmit antenna pattern selected from a predetermined set of transmit antenna patterns. The second device waits for a response from the first device. The first device cycles through its different receive patterns (i.e., directions) in each time slot.
According to another aspect of the disclosure, a method of communication is provided for allowing access to the centralized contention period by one or more wireless devices (e.g., a second wireless device) that communicate with a first wireless device (e.g., a master device) using a directional slotted ALOHA protocol. The second device maintains a set of N back-off window sizes equal in number to the first device's number N of receive directions. The second device may draw a set of N random numbers between one and the back-off window size(s). Each random number indicates a particular time cycle and time slot within the time cycle, which provides a period of time that the second device waits before transmitting the frame. Each time cycle comprises N time slots, and the selection of a time slot in a time cycle may be determined by the random number index in the set of the N random numbers.
According to another aspect of the disclosure, a method of communication is provided for accessing a centralized contention period that is used to communicate with a first wireless device (a master device) using a directional cycle-based ALOHA protocol. A second wireless device transmits a frame in the first time slot of a time cycle using one of a plurality of transmit antenna patterns from a set and waits for a response from the first device, which uses a first receive direction in the first time slot. The second device transmits the frame in the second time slot of a time cycle using the same transmit antenna pattern and waits for a response from the first device, which employs a second receive direction in the second time slot. The second device employs successive (e.g., sequential) time slots of a time cycle for transmitting the frame until it successfully decodes a response back from the first device, or until it has transmitted the frame in all N time slots.
According to another aspect of the invention, the centralized contention period may be used for authentication, association, service period requests, data communications, and/or direction acquisition and tracking Each time slot has a fixed duration, the time slot duration being at least equal to the duration of a transmit request frame, a first guard period (commonly known as an SIFS (Short Inter Frame Spacing)), the duration of a response frame, and a second guard period (e.g., a second SIFS).
According to another aspect of the disclosure, a communications method comprises transmitting a service period request (also known as a channel time allocation request) from a second wireless device to a first wireless device, wherein the service period request is transmitted using the directional slotted ALOHA protocol; receiving a service period allocation granted by the first device and transmitted using a second transmit pattern; and transmitting at least one frame from the second device to a destination device in the service period.
According to another aspect of the disclosure, a method of communication comprises employing at least one of a full double sweep and a partial double sweep for finding a pair of downlink working directions.
The partial double sweep comprises transmitting a set of request frames one at a time using a directional ALOHA protocol, in a first transmit direction from a second wireless device to a first wireless device. The first device changes its receive direction from one time slot to another in a cyclic manner (i.e., the first device repeats the same N receive directions in each time cycle). The second device listens for a response from the first device. If no response is detected, the second device sends a set of request frames using a second transmit direction one at a time using the directional ALOHA protocol, and the process of sending request frames and listening for a response may be repeated for up to all possible transmit directions or until the second device successfully detects a response from the first device. The second device uses the direction(s) for which it successfully decoded a response from the first device as a working direction(s) that it uses for further communications with the first device.
The full double sweep comprises transmitting a set of request frames, one at a time using the directional ALOHA protocol, in a first direction from the second device to the first device. The first device changes its receive direction from one time slot to another in a cyclic manner. The second device sends another set of request frames in a second transmit direction to the first device, one at a time using the directional ALOHA protocol. The process of sending request frames is repeated for all transmit directions of the second device. The second device selects the direction(s) with the highest link quality indicator (LQI) as a preferred direction(s) for communicating with the first device.
In accordance with one aspect of the invention, a wireless system comprises means for selecting a sequence of time slots paired with a plurality of transmit directions for transmitting at least one request frame from a first wireless device to a second wireless device; means for listening for the at least one request frame at the second wireless device by employing a different one of a plurality of receive directions in each of the time slots; means for transmitting at least one response frame from the second wireless device to the first wireless device; means for listening for the at least one response frame at the first wireless device; and means for selecting a preferred set of uplink and downlink directions for further communication between the first wireless device and the second wireless device. Means for selecting the sequence of time slots may include, by way of example, but without limitation, a digital computer system comprising a memory for storing instructions and a processor for executing the instructions. Means for listening may include, by way of example, but without limitation, any wireless radio receiver employing directional beam patterns and configured to detect, demodulate, and/or decode received transmissions. Means for transmitting may include, by way of example, but without limitation, any wireless radio transmitter employing directional beam patterns and configured for generating a response frame and other data signals, and coupling data signals into a wireless communication channel. Means for selecting a preferred set of uplink and downlink directions may include, by way of example, but without limitation, a digital computer system comprising a memory for storing instructions and a processor for executing the instructions, and may share one or more components used by the means for selecting the sequence of time slots.
In accordance with another aspect of the invention, a wireless device comprises means for selecting a sequence of time slots paired with a plurality of transmit directions for transmitting at least one request frame from the first wireless device to a second wireless device, the second wireless device employing a different one of a plurality of receive directions for each of the time slots; means for listening for at least one response frame transmitted by the second wireless device; and means for selecting a preferred set of uplink and downlink directions for further communication between the first wireless device and the second wireless device. Means for selecting the sequence of time slots may include, by way of example, but without limitation, a digital computer system comprising a memory for storing instructions and a processor for executing the instructions. Means for listening may include, by way of example, but without limitation, any wireless radio receiver employing directional beam patterns and configured to detect, demodulate, and/or decode received transmissions. Means for selecting a preferred set of uplink and downlink directions may include, by way of example, but without limitation, a digital computer system comprising a memory for storing instructions and a processor for executing the instructions, and may share one or more components used by the means for selecting the sequence of time slots.
In accordance with another aspect of the invention, a wireless device comprises means for employing a different one of a plurality of receive directions for each of a sequence of time slots to listen for at least one request frame transmitted by a second wireless device; means for transmitting at least one response frame to the second wireless device in response to a received request frame; and means for selecting a preferred set of uplink and downlink directions for further communication between the first wireless device and the second wireless device. Means for employing a different one of a plurality of receive directions for each of a sequence of time slots to listen for at least one request frame transmitted by a second wireless device may include, by way of example, but without limitation, any wireless radio receiver employing directional beam patterns and configured to detect, demodulate, and/or decode received transmissions. Means for transmitting may include, by way of example, but without limitation, any wireless radio transmitter employing directional beam patterns and configured for generating a response frame and other data signals, and coupling data signals into a wireless communication channel. Means for selecting a preferred set of uplink and downlink directions may include, by way of example, but without limitation, a digital computer system comprising a memory for storing instructions and a processor for executing the instructions.
In accordance with another aspect of the invention, a wireless device comprises means for generating a plurality of time cycle numbers, the plurality of time cycle numbers being equal to a plurality of receive directions employed by a second wireless device, each of the time cycle numbers being associated with one of the receive directions and having a value within a predetermined back-off window size; means for sequentially organizing the plurality of time cycle numbers with respect to their values for producing a sequence of time cycle numbers; means for generating a sequence of time slot numbers from the sequence of time cycle numbers and the plurality of receive directions, the sequence of time slot numbers being used to select time slots for transmitting a frame to the second wireless device. Means for generating the plurality of time cycle numbers, means, means for sequentially organizing the plurality of time cycle numbers, and means for generating the sequence of time slot numbers may include, by way of example, but without limitation, a digital computer system comprising a memory for storing instructions and a computer processor for executing the instructions.
So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description, briefly summarized above, may be had by reference to aspects, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only certain typical aspects of this disclosure and are therefore not to be considered limiting of its scope, for the description may admit to other equally effective aspects.
Various aspects of the disclosure are described more fully hereinafter with reference to the accompanying drawings. This disclosure may, however, be embodied in many different forms and should not be construed as limited to any specific structure or function presented throughout this disclosure. Rather, these aspects are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Based on the teachings herein one skilled in the art should appreciate that the scope of the disclosure is intended to cover any aspect of the disclosure disclosed herein, whether implemented independently of or combined with any other aspect of the disclosure. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, the scope of the disclosure is intended to cover such an apparatus or method which is practiced using other structure, functionality, or structure and functionality in addition to or other than the various aspects of the disclosure set forth herein. It should be understood that any aspect of the disclosure disclosed herein may be embodied by one or more elements of a claim.
The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects.
Although particular aspects are described herein, many variations and permutations of these aspects fall within the scope and spirit of the disclosure. Although some benefits and advantages of the preferred aspects are mentioned, the scope of the disclosure is not intended to be limited to particular benefits, uses, or objectives. Rather, aspects of the disclosure are intended to be broadly applicable to different wireless technologies, system configurations, networks, and transmission protocols, some of which are illustrated by way of example in the figures and in the following description of the preferred aspects. The detailed description and drawings are merely illustrative of the disclosure rather than limiting, the scope of the disclosure being defined by the appended claims and equivalents thereof. AN EXAMPLE WIRELESS COMMUNICATION SYSTEM
The techniques described herein may be used for various broadband wireless communication systems, including communication systems that are based on a single carrier transmission and OFDM. Aspects disclosed herein may be advantageous to systems employing Ultra Wide Band (UWB) signals including millimeter-wave signals, Code Division Multiple Access (CDMA) signals, and OFDM. However, the present disclosure is not intended to be limited to such systems, as other coded signals may benefit from similar advantages.
Under IEEE 802.11 and 802.15, one STA assumes the role of a coordinator (master) of the BSS. This coordinating STA is referred to as a Service Access Point (SAP) and is illustrated in
A variety of algorithms and methods may be used for transmitting information in the wireless communication system 100 between the SAPs 104 and the STAs 106 and between the STAs 106 themselves. For example, signals may be communicated between the SAPs 104 and the STAs 106 in accordance with a CDMA technique and signals may be sent and received between STAs 106 in according with an OFDM technique. If this is the case, the wireless communication system 100 may be referred to as a hybrid CDMA/OFDM system.
A communication link that facilitates transmission from an SAP 104 to an STA 106 may be referred to as a downlink (DL) 108, and a communication link that facilitates transmission from an STA 106 to an SAP 104 may be referred to as an uplink (UL) 110. Alternatively, a downlink 108 may be referred to as a forward link or a forward channel, and an uplink 110 may be referred to as a reverse link or a reverse channel. When two STAs communicate directly with each other, a first STA will act as the master of the link, and the link from the first STA to the second STA will be referred to as the downlink 112, and the link from the second STA to the first STA will be referred to as the uplink 114.
A BSS 102 may be divided into multiple sectors. A sector 116 is a physical coverage area within the BSS 102. SAPs 104 within the wireless communication system 100 may utilize antennas that concentrate the flow of power within a particular sector 116 of the BSS 102. Such antennas may be referred to as directional antennas.
The wireless device 202 may include a processor 204 that controls operation of the wireless device 202. The processor 204 may also be referred to as a central processing unit (CPU). Memory 206, which may include one or both read-only memory (ROM) and random access memory (RAM), provides instructions and data to the processor 204. A portion of the memory 206 may also include non-volatile random access memory (NVRAM). The processor 204 typically performs logical and arithmetic operations based on program instructions stored within the memory 206. The instructions in the memory 206 may be executable to implement the methods described herein.
The wireless device 202 may also include a housing 208 that may include a transmitter 210 and a receiver 212 to allow transmission and reception of data between the wireless device 202 and a remote location. The transmitter 210 and receiver 212 may be combined into a transceiver 214. An antenna 216 may be attached to the housing 208 and electrically coupled to the transceiver 214. The wireless device 202 may include one or more wired peripherals 224 such as USB, HDMI, or PCIE. The wireless device 202 may also include (not shown) multiple transmitters, multiple receivers, multiple transceivers, and/or multiple antennas.
The wireless device 202 may also include a signal detector 218 that may be used to detect and quantify the level of signals received by the transceiver 214. The signal detector 218 may detect such signals as total energy, energy per subcarrier per symbol, power spectral density, and/or other signal measurements that are known in the art. The wireless device 202 may also include a digital signal processor (DSP) 220 for processing signals.
The various components of the wireless device 202 may be coupled together by a bus system 222, which may include a power bus, a control signal bus, and a status signal bus, in addition to a data bus.
Data 306 to be transmitted are shown being provided as input to a forward error correction (FEC) encoder 308. The FEC encoder 308 encodes the data 306 by adding redundant bits. The FEC encoder 308 may encode the data 306 using a convolutional encoder, a Reed Solomon encoder, a Turbo encoder, a low density parity check (LDPC) encoder, etc. The FEC encoder 308 outputs an encoded data stream 310. The encoded data stream 310 is input to a mapper 314. The mapper 314 may map the encoded data stream onto constellation points. The mapping may be done using some modulation constellation, such as binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), 8 phase-shift keying (8PSK), quadrature amplitude modulation (QAM), constant phase modulation (CPM), etc. Thus, the mapper 312 may output a symbol stream 314, which may represents one input into a block builder 310. Another input in the block builder 310 may include one or more spreading codes produced by a spreading code generator 318.
The block builder 310 may be configured for partitioning the symbol stream 314, into sub-blocks and creating OFDM/OFDMA symbols or single-carrier sub-blocks. The block builder 310 may append each sub-block with a guard interval, a cyclic prefix, or a spreading sequence from the spreading codes generator 318. Furthermore, the sub-blocks may be spread by one or multiple spreading codes from the spreading code generator 318.
Output signal 320 may be pre-pended by a preamble 322 generated from one or more spreading sequences from the spreading code generator 324. The output stream 326 may then be converted to analog and up-converted to a desired transmit frequency band by a radio frequency (RF) front end 328, which may include a mixed signal section and an analog section. An antenna 330 transmits the resulting signal 332.
The transmitted signal 332 is shown traveling over a wireless channel 334. When a signal 332′ is received by an antenna 330′, the received signal 332′ may be down-converted to a baseband signal by an RF front-end 328′ which may include a mixed signal and an analog portion. Preamble detection and synchronization component 322′ may be used to establish timing, frequency and channel synchronization using one or multiple correlators that correlate with one or multiple spreading codes generated by a spreading code generator 324′.
The output of the RF front end block 328′ is input to the frequency and timing correction component 326′ along with the synchronization information from component 322′. The outputs from components 326′ and 322′ are input to a block detection component 316′. When OFDM/OFDMA is used, the block detection may include cyclic prefix removal and fast Fourier transform (FFT). When single-carrier transmissions are used, the block detection may include de-spreading and equalization.
A de-mapper 312′ may perform the inverse of the symbol mapping operation performed by the mapper 312, thereby outputting soft and/or hard decisions 310′. The soft and/or hard decisions 310′ are input to the FEC decoder 308′, which provides a stream of data estimates 306′. Ideally, this data stream 306′ corresponds to the data 306 that was input to the transmitter 302.
The wireless system 100 illustrated in
A Contention Based Period (CBP) 420 is used to communicate command, control, management, and data frames either between the SAP 104 and at least one of the plurality of STAs 106 in the network 100, or between any set of STAs 106 in the network 100. The access method for the CBP 420 may be based on a slotted ALOHA or a carrier sense multiple access with collision avoidance (CSMA/CA) protocol.
A Channel Time Allocation Period (CTAP) 430, which is based on a Time Division Multiple Access (TDMA) protocol, is provided by the SAP 104 to allocate time for the plurality of STAs 106 to use the channels in the network 100. Specifically, the CTAP is divided into one or more time periods (of different sizes), referred to as Channel Time Allocations (CTAs). The CTAs, also known as Service Periods (SPs), are typically allocated by the SAP 104 to pairs of stations, one pair of stations to a CTA. Thus, the access mechanism for CTAs is TDMA-based.
Referring to
The packet sync sequence field 458 is a repetition of ones (or a repetition of minus ones, or an alternating sequence of ones and minus ones) spread by one of the length-128 complementary Golay codes (a128, b128) as represented by codes 464-1 to 464-Q in
In one aspect of the disclosure, a dual-mode millimeter wave system employing single-carrier modulation and OFDM is provided with a single-carrier common-mode signaling. The common mode, also known as control PHY (Physical layer), is a single-carrier mode used by both single-carrier and OFDM devices for beaconing, signaling (such as control and management), beamforming, and base-rate data communications.
Directional Aloha ProtocolIn typical systems, an SAP transmits a single beacon frame in the beacon period (BP) 410, such as depicted in
According to one aspect of the invention, during the beacon interval 410 in
For an SAP that is omni-capable on transmission (i.e., an SAP with a single antenna pattern covering the region of interest), M=1. For an SAP with sectorized antennas, M is the number of sectors that the SAP is able to support. Similarly, when an SAP is provided with switching transmit diversity antennas, M may represent the number of transmit antennas in the SAP. Various approaches to the structure of the Q-omni beacon frame may be used.
The following disclosure relates to the general case of stations (STAs), including SAPs, having transmit directions and receive directions that may be different (referred to as asymmetric STAs). Stations having identical transmit directions and receive directions (referred to as symmetric STAs) are a special case.
As discussed above, a SAP broadcasts a set of M beacon frames, typically in every superframe. Each beacon frame contains all timing information about the superframe and, optionally, information about some or all of the STAs that are members of the BSS, including the beamforming capabilities of each STA. The STA beamforming capabilities are obtained by the SAP during association. An STA beamforming capability includes a number of transmit and receive directions. An STA may use a different number of transmit and receive directions for different tasks. For example, the number of directions could be a number of antennas for an STA with switched antennas, a number of sectors for an STA with sectored antennas, or a number of coarse patterns for an STA with a phase antenna array. A phased antenna array can generate a set of patterns that may overlap, each pattern covering a part of the region of the space of interest.
The following notation is used to clarify different aspects of the disclosure. Let M and N be the total number of SAP's transmit and receive antenna patterns, respectively, and let P and Q be the total number of an STA's transmit and receive antenna patterns respectively. As mentioned above, the number of directions M, N, P, and Q may be changed. As an example, an STA may use P=2 directions during association and P=16 directions in a CTAP. Furthermore, an STA may initially use a coarse number of broad directions and adapt either or both the directions and the number of directions to provide a set of fine directions.
An STA may perform the following steps in order to associate (i.e., become a member of the BSS) with the SAP. First, the STA searches for a beacon from the SAP. The STA then detects at least one of the M directional beacon frames and acquires knowledge of the superframe timing, the number of the SAP's transmit and receive directions (i.e. M and N), duration of the CBP, and, optionally, the possible capabilities of each of the STA members. In an aspect of the disclosure, the STA acquires and tracks the best SAP transmit direction by measuring a link quality indicator (LQI) from all K directional beacon packets transmitted by the SAP. In one aspect of the disclosure, the LQI is a metric of the quality of the received signal. Examples of an LQI include, but are not limited to, an RSSI (Received Signal Strength Indicator), an SNR (Signal to Noise Ratio), an SNIR (Signal to Noise and Interference Ratio), an SIR (Signal to Interference Ratio), a preamble detection, a BER (Bit Error Rate), and a PER (Packet Error Rate).
According to one aspect of the disclosure, an STA may detect a beacon packet by sweeping over its set of N receive directions over one or more superframes. Upon detection of at least one of the beacon packets, the STA acquires a vast amount of information. For example, the STA may acquire knowledge of the following: a) the SAP's number of transmit and receive directions during beaconing (i.e., M and N); b) the index of SAP's preferred transmit direction (e.g., the beacon packet with the highest LQI) from the SAP to the STA, referred to as the SAP's transmit direction number m. Direction number m is acquired by the STA by sorting the LQIs from the M beacon frames transmitted by the SAP in different directions and received by the STA using its Q receive directions. There are M×Q combinations in total, and one combination yields a best LQI. Alternatively, the STA may use the direction corresponding to the first beacon frame it successfully detects as its preferred direction; c) the index of the STA's preferred receive direction when listening to the SAP. The STA's preferred receive direction is referred to as direction q; d) the list of devices that are members of the current BSS, and some or all of their capabilities in terms of PHY support (single carrier support or OFDM support, data rates, number of transmit and receive directions, etc.); e) the structure and duration of different fields of the superframe, such as the start time of CBP, duration of the CBP, superframe duration, etc.; and f) the time allocations of SPs in the CTAP.
Upon detection of the beacon, the STA goes through the association process to become a member of the BSS. After association, the STA may exchange data packets with another STA or with the SAP in accordance with one of two procedures. In accordance with a first procedure, the STA may access the contention-based period using a slotted ALOHA protocol or a carrier sense multiple access with collision avoidance CSMA/CA protocol in a manner similar to that specified in the IEEE 802.11 protocol. In accordance with a second procedure, the STA requests a service period (SP) from the SAP for the purpose of exchanging data packets with another STA. If the request is accepted by the SAP, the SAP grants access to the demanding STA and broadcasts a time allocation in the beacon. The SAP may provide information about the source STA and address STA(s). The source and destination STAs may then exchange data packets in the dedicated time allocated service period.
The association process involves transmitting an association request from the STA to the SAP, and transmitting an association response from the SAP to the STA. This process may involve exchanges of many frames before the STA is considered to be associated. Furthermore, an STA might have to be authenticated prior to association. Authentication may be part of the association process.
For networks such as IEEE 802.11, the SAP and STAs have a single transmit antenna pattern, and the association process is relatively simple and straightforward. IEEE 802.11 uses a CSMA/CA protocol. To clarify the association process, a simple slotted ALOHA protocol is shown in
For directional STAs and/or SAPs, the previously described slotted ALOHA procedure may not perform well, especially when an STA does not know which direction to use for transmissions to the SAP and the SAP does not know which direction to use for reception. The same problem occurs with CSMA/CA, since good STA-to-SAP and SAP-to-STA directions are not known at either side of the link. Furthermore, the hidden-node problem is worse, since stations cannot hear each other due to their directional antenna patterns. In addition, the problem is more severe if the contention based period is used for direction finding, authentication, association, service period (time allocation) request, data frame exchange between peer-to-peer STAs, and data frame exchanges between the STA and SAP.
According to one aspect of the invention, the contention based period is divided into two portions, a centralized contention based period (C-CBP) 620 and a distributed contention based period (D-CBP) 630, such as shown in
In the following, a frame transmission from an STA to the SAP is referred to as a request frame, and frame transmission from the SAP to an STA is referred to as a response frame.
In one aspect of the invention, the centralized contention based period is divided into equal-size slots, such as shown in
In
According to one aspect of the invention, an SAP may specify fixed time-cycle boundaries where the first time cycle boundary coincides with the first time slot in the C-CBP. According to another aspect of the invention, an SAP may leave the choice of time-cycle boundaries to different STAs. As an example, an STA might choose a time cycle as time slots 664-1-2 to and including 664-2-1. That is, from an STA's perspective, a time cycle comprises N consecutive time slots, such as time slots 1 to N, or time slots 2 to N+1, or time slots 3 to N+2, etc.
Before using the C-CBP, an STA acquires the beacon, such as described previously. After beacon detection, an SAP acquires knowledge of its preferred SAP transmit direction number m (i.e., the preferred SAP-to-STA transmit direction). The STA determines its preferred receive direction number q by listening to the SAP. Therefore, before using the C-CBP, an STA is equipped with the SAP's preferred transmit direction m and its preferred receive direction n. The values m and q are the preferred uplink pair of directions.
According to one aspect of the invention, an STA uses the same transmit direction for each set of N consecutive time slots. This set of N-consecutive time slots may (but not necessarily) be aligned with a time cycle, such as cycles 662-1 to 662-S. For example, if there is only one STA in the network, the STA may transmit a first request frame using its transmit direction #1 in a time slot number 1 and then waits for a response. During this time slot, the SAP uses its receive direction number 1. If no response is detected by the STA, one of the reasons may be that the combination of STA transmit direction number 1 and SAP receive direction number 1 does not have enough LQI. The STA transmits a second request frame in time-slot number 2 while still using its transmit direction number 1, but the SAP employs its receive direction number 2. If the STA does not detect a response, it continues transmitting request frames using the same transmit direction number 1 for each of the N time slots or until a response is detected. If no response is received by the STA after transmitting in the N time slots, the STA uses transmit direction number 2 for the next N time slots or until a response is received. This process may be repeated for each of the STA's transmit directions or until a response is received. Such a process is referred to as a double sweep, wherein the SAP sweeps (i.e., changes its direction) on a time-slot basis (i.e., the SAP's receive direction changes every time slot). The STA sweeps on a cycle basis, that is, it changes its transmit direction every time cycle (i.e., N time slots). This double sweep is illustrated in
According to another aspect of the invention, each request frame sent by the STA comprises information regarding the SAP's preferred transmit direction m. As described above, the STA determines the SAP's preferred transmit direction from the beacon detection and monitoring stage. Once the SAP detects and decodes a request frame sent by an STA, it determines which transmit direction to use for transmitting the response frame to the STA.
Once a response frame is detected by the STA, the STA and SAP have a working pair of directions in both downlink and uplink. That is, the STA determines a working transmit direction toward the SAP and a preferred receive direction when receiving from the SAP. The STA's working transmit direction is not necessarily the best direction. Rather, it may be the first direction that results in a successful transaction (transmission/reception) with the SAP.
The previous aspect of the invention was explained in reference to a single STA communicating with the SAP. When multiple stations contend to access the C-CBP, collisions occur. Therefore, there is a need for a back-off procedure that accounts for the directivity of the stations.
According to one aspect of the invention, an STA uses a set of N random back-off numbers R(1), R(2), . . . , R(N) for determining the number of back-off time slots (or equivalently, time cycles and time slots within the time cycles) before transmission corresponding to the N SAP receive directions. The nth random number R(n) indicates the number of back-off time slots for a given target SAP receive direction number (i.e., when the SAP employs its receive direction number n). Therefore, the candidate time slots to be considered for back-off random number R(n) are the time slots where the SAP's receive direction is denoted by direction number n. For example, in reference to the numbering scheme in
According to one aspect of the invention, an STA that needs to transmit in the C-CBP draws a set of N random numbers R(1), R(2), . . . , R(N), where R(n) is between 1 and W(n) for n=1, 2, . . . , N. As explained above, the random number R(n) determines the number of back-off time cycles, and the target time slot is the nth time slot in cycle number R(n). According to one aspect of the invention, the STA sorts the set of random numbers in ascending order R[t(1)]≦R[t(2)]≦ . . . ≦R[t(N)], where t(1) is the index of the smallest random number, t(2) is the index of the second smallest random number and so on. The first request frame is transmitted using transmit direction number t(1) in the t(1)th time-slot number in cycle number R[t(1)]; that is, in time-slot number {R[t(1)]−1}×N+t(1) if the time slots are numbered 1, 2, 3, . . . from the boundary of the C-CBP, such as shown in
Aspects of the invention are further described with reference to
According to one aspect of the invention, upon a successful transaction, the STA uses the pair of working directions in which the successful transaction occurred for future communication with the SAP. If, for example, the third transaction was successful, then according to another aspect of the invention, the STA contends only in slots number 3*n for n=1, 2, 3, . . . . That is, if the STA needs to send a request frame in the next superframe, the only candidate slots for possible transmissions are time-slots number 3, 6, 9, 12, 15, 18, 21, and 24. The STA uses a single back-off window size W=W(3) and a single random number R=R(3) to access the C-CBP. Furthermore, the STA uses the same transmit direction it used during the successful transaction. In summary, upon a successful transaction, the STA has knowledge of the following: a) A working transmit direction toward the SAP, referred to as STA transmit direction number p; b) an SAP working receive direction, referred to as the SAP receiver direction number n; c) the STA's preferred receive direction from the SAP, referred to as the STA receive direction number q; and d) the SAP's preferred transmit direction to the STA, referred to as the SAP transmit direction number m. The STA uses this pair of downlink and uplink directions for further communication with the SAP.
According to one aspect of the invention, after a successful transaction with an STA, such as described above, the SAP stores a preferred transmit direction to the STA and, optionally, a working receive direction from the STA. Furthermore, the STA stores a preferred receive direction from the SAP and a working transmit direction toward the SAP.
According to one aspect of the invention, the STA may use the C-CBP to find a preferred downlink using the directional back-off procedure described above. Upon a successful transaction with the SAP, the SAP has a working downlink pair of directions (i.e., the STA working transmit direction number p and the SAP working receive direction number n). This pair of working downlink directions is not necessarily the best pair of directions. The SAP has N receive directions and the STA has P transmit directions. In some aspects of the invention, the SAP surveys all direction combinations (i.e., N×P directions) and the SAP measures the LQI for each combination (nc,pc), where nc=1 to N and pc=1 to P, to find a preferred pair of downlink directions. Upon a first successful transaction, the STA will have tried the following combinations: a) N transactions in N times-slots in which the STA uses direction number 1 and the SAP cycles through its N directions one at a time per time slot; b) N transactions in N times-slots in which the STA uses direction number 2 and the SAP cycles through its N directions one at a time per time slot; c) p−1 transactions in N times-slots in which the STA uses direction number p−1 and the SAP cycles through its N directions one at a time per time slot; and d) n time slots in which the STA uses direction number p and the SAP cycles through directions 1 to n, where in the last time slot, the working pair of directions (the STA transmit direction number p and the SAP receive direction number m) were found. Therefore, the STA has gone through N×(p−1)+n transactions where only the last one was successful. The STA may choose to continue the procedure, that is, the remaining N×P−[N×(p−1)×n] combinations of directions, using the above directional exponential back-off procedure in order to find a preferred downlink pair with a preferred LQI. If the STA completes its trial of all N×P directions, this is a full double sweep. Otherwise, if the STA stops at the first working downlink pair of directions, it is a partial successful double sweep.
According to one aspect of the invention, if an STA performs a full double sweep, the SAP measures the LQI for each successful reception of a request frame and sends the LQI as a feedback in one of the fields of the response frame. Furthermore, the STA may sort LQIs (either all LQIs or just those above a given threshold) and select at least one preferred downlink pair for further transactions with the SAP. The preferred uplink pair is obtained from the beacon frames, as explained above, and may not be part of the C-CBP direction search.
According to one aspect of the invention, if an STA performs a full double sweep, the SAP measures the LQI for each successful reception of a request frame and sends the LQI as a feedback in one of the fields of the response frame. Furthermore, the SAP may sort LQIs (either all LQIs or just those above a given threshold) and then provide feedback to the STA. The STA may select the preferred downlink pair for further transactions with the SAP. The preferred uplink pair is obtained from the beacon frames, as explained above, and may not be part of the C-CBP direction search.
According to one aspect of the invention, upon finding a working or preferred pair of uplink and downlink directions (the SAP's transmit direction number, m, the SAP's receive direction number, n, the STA's transmit direction number, p, and the STA's receive direction number, q) an STA having a request frame to send may use a single back-off window size, W, and a single uniform number generator. According to one aspect of the invention, the STA generates a uniform random number R in the range 1 to W and uses the nth time slot in time-cycle number Z to transmit the request frame using transmit direction number p. If this is the first attempt by the STA to transmit the request frame, then Z=R. if this is not the first attempt by the STA to transmit the request frame, then Z=R+R
In the case in which an STA is moving, the preferred or working pair of downlink directions may change.
According to another aspect of the invention, after a full or partial successful double sweep, an STA keeps a list of K downlink direction pairs (for example, a best pair and a second-best pair) and tracks and update the list by using the directional back-off algorithm in the appropriate time slots. In one aspect of the invention, 2 pairs are maintained; a best pair (p1,n1) of downlink directions and a second-best pair (p2,n2), where the first index (p1 or p2) refers to the STA transmit direction number and the second index (n1 or n2) refers to the SAP receive direction number. The STA may determine the LQI of its best transmit direction (measured by the SAP and sent back to the STA in the response frame) in every superframe and determine the LQI of the second best transmit direction (measured by the SAP and sent back to the STA in the response frame) during every other superframe. So according to another aspect of the invention, the tracking of the downlink direction pairs occurs at different update rates. When the STA updates the LQI of the best downlink direction pair (p1,n1), it may use the directional exponential back-off algorithm. For example, the STA uses a back-off window size W1 and draws a random number R1(1), where R1(1) is between 1 and W1. The STA sends a request frame in the n1th slot of cycle number R1 (i.e., in slot number [R1(1)−1]×N+n1). The request frame contains information about the SAP's preferred transmit direction n1 from the STA's perspective, information that is available to the STA as a result of decoding and tracking the beacon frames. The SAP receives the request frame using direction number n1, measures the LQI of the request, and send the LQI back to the STA in the response frame. The SAP transmits the response frame using transmit direction number n1, and the STA receives the response using receive direction number q. Furthermore, the STA may update its list after each feedback or at the end of the double sweep. The request packet and response packet may be sounding packets, which are specialized packets used for measuring and reporting channel conditions and LQI. If the STA does not receive the response packet, or the response packet was not correctly decoded, the STA doubles the back-off window size W1, draws a random number R1(2), and a second attempt is initiated by sending a request frame in the n1th time slot of cycle number [R1(1)+R1(2)], that is, in slot number [R1(1)+R1(2)−1]×N+n1. The STA waits for a response, and if the response packet is decoded correctly, the STA receives the LQI (which was sent in the response frame by the SAP) and updates its list of K downlink direction pairs. Each item of the list may simply contain the pair of directions (p,n) or the index p, and the corresponding LQI measured by the SAP. In the event of a predetermined number of unsuccessful transactions for the pair (p1,n1), the STA may remove the pair (p1,n1) from the list and select (p2,n2) as an alternative or temporary preferred pair until a better pair is found.
According to one aspect of the invention, if during or after updating the STA's list of K downlink direction pairs, a better downlink direction pair is discovered, the STA may select the better downlink direction pair for further transactions with the SAP.
According to one aspect of the invention, the C-CBP is used for at least one of STA authentication, association, transmit and/or receive direction finding, direction tracking, control frames, service period reservation, command frames, management frames, and data frames, where in all cases, the communication is between the STA and the SAP. An STA may use the directional slotted-ALOHA protocol in the C-CBP to exchange data frames with the SAP. However, the length of the data frames should be selected such that a transaction does not exceed the slot boundary. If the frame is too long, it should be adapted to fit within a time slot along with the response and two SIFS. As another example of a data transaction, the request frame may be a data frame and the response frame may be an immediate acknowledgment. For association, the request frame may be an association request and the response frame may be an association response. Peer-to-peer communications in which neither peer is an SAP is preferably performed in the D-CBP. As another example, the request frame can be a service period reservation request by an STA, and the response frame sent by the SAP may be the SAP denial or acceptance of the service period reservation. Each task (such as association, authentication, service period reservation, etc.) may require more than a simple exchange of two frames (i.e., the request frame and response frame). Rather, a task may require multiple request-response frames. Direction finding may be performed using a full double sweep or a partial successful double sweep. The direction acquisition (finding) can be performed as part of authentication and/or association, or it may be performed independently. When performed independently, it is preferably done before any other task in the C-CBP, such as before authentication, association, and data exchange. If the direction acquisition is accomplished as an independent STA task, the request and response frames used during the sweep may be specialized sounding packets. Alternatively, if the direction acquisition is part of authentication, then the request and response frames are authentication request and response frames.
According to another aspect of the invention, a directional cycle-based ALOHA method is employed wherein the directional exponential back-off is cycle-based rather than slot-based. Specifically, an STA may use a single back-off window size W and a single random number R. The STA generates a random number R1 (1≦R1≦W) that is used for the first N candidate transmissions in N time slots in cycle number R. The STA transmits a first request frame using transmit direction number 1 in the first time slot of time-cycle number R. During the first time slot, the SAP employs its first receive direction. If the STA does not receive a response, the transaction is unsuccessful, so the STA transmits a second request frame in transmit direction number 1 in the second time slot of time-cycle number R. The SAP employs its second receive direction in the second time slot, and the STA listens for a response. This process may be repeated for all N time slots within the time-cycle number R. If there are no successful transactions, the STA doubles its back-off window and generates a second random number R2 (1≦R2≦2W). The random number R2 is used for the second set of N scheduled transmissions in N time slots in cycle number R1+R2, and the STA repeats its transmission process using transmit direction number 2. This process may be repeated for all the STA transmit directions.
An STA may use both directional cycle-based ALOHA and directional slot-based ALOHA. As an example, an STA may use cycle-based ALOHA for initial direction acquisition (e.g., direction-finding) during a partial or full double sweep. In this case, an STA may finish the double sweep in P (non-consecutive) cycles such that within each time cycle, the STA employs a fixed transmit direction and the SAP sweeps over all of its receive directions, one receive direction per time slot. When a preferred downlink pair of directions is found, the pair may be used for authentication, association, and further data transfer with a directional slotted ALOHA protocol, as previously described.
The various operations of methods described above may be performed by any suitable means capable of performing the corresponding functions. The means may include various hardware and/or software component(s) and/or module(s), including, but not limited to a circuit, an application specific integrated circuit (ASIC), or processor. Generally, where there are operations illustrated in Figures, those operations may have corresponding counterpart means-plus-function components with similar numbering. For example, blocks 902-906, 942-946, 1002-1008, 1042-1046, 1102-1110 1202-1208, and 1302-1306, illustrated in
As used herein, the term “determining” encompasses a wide variety of actions. For example, “determining” may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database or another data structure), ascertaining and the like. Also, “determining” may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory) and the like. Also, “determining” may include resolving, selecting, choosing, establishing and the like.
The various operations of methods described above may be performed by any suitable means capable of performing the operations, such as various hardware and/or software component(s), circuits, and/or module(s). Generally, any operations illustrated in the Figures may be performed by corresponding functional means capable of performing the operations.
The various illustrative logical blocks, modules and circuits described in connection with the present disclosure may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array signal (FPGA) or other programmable logic device (PLD), discrete gate or transistor logic, discrete hardware components or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any commercially available processor, controller, microcontroller or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.
The steps of a method or algorithm described in connection with the present disclosure may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in any form of storage medium that is known in the art. Some examples of storage media that may be used include random access memory (RAM), read only memory (ROM), flash memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CDROM and so forth. A software module may comprise a single instruction, or many instructions, and may be distributed over several different code segments, among different programs, and across multiple storage media. A storage medium may be coupled to a processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor.
The methods disclosed herein comprise one or more steps or actions for achieving the described method. The method steps and/or actions may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the claims.
The functions described may be implemented in hardware, software, firmware or any combination thereof. If implemented in software, the functions may be stored as one or more instructions on a computer-readable medium. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Disk and disc, as used herein, include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers.
Thus, certain aspects may comprise a computer program product for performing the operations presented herein. For example, such a computer program product may comprise a computer readable medium having instructions stored (and/or encoded) thereon, the instructions being executable by one or more processors to perform the operations described herein. For certain aspects, the computer program product may include packaging material.
Software or instructions may also be transmitted over a transmission medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of transmission medium.
Further, it should be appreciated that modules and/or other appropriate means for performing the methods and techniques described herein can be downloaded and/or otherwise obtained by a user terminal and/or base station as applicable. For example, such a device can be coupled to a server to facilitate the transfer of means for performing the methods described herein. Alternatively, various methods described herein can be provided via storage means (e.g., RAM, ROM, a physical storage medium such as a compact disc (CD) or floppy disk, etc.), such that a user terminal and/or base station can obtain the various methods upon coupling or providing the storage means to the device. Moreover, any other suitable technique for providing the methods and techniques described herein to a device can be utilized.
It is to be understood that the claims are not limited to the precise configuration and components illustrated above. Various modifications, changes and variations may be made in the arrangement, operation and details of the methods and apparatus described above without departing from the scope of the claims.
The techniques provided herein may be utilized in a variety of applications. For certain aspects, the techniques presented herein may be incorporated in a base station, a mobile handset, a personal digital assistant (PDA) or other type of wireless device that operate in UWB part of spectrum with processing logic and elements to perform the techniques provided herein.
Claims
1. A digital computer network comprising:
- a first transmitter component residing on a first wireless device employing a sequence of time slots paired with a plurality of transmit directions for transmitting at least one request frame to a second wireless device;
- a first receiver component residing on the first wireless device configured for receiving at least one response frame from the second wireless device;
- a second receiver component residing on the second wireless device employing a different one of a plurality of receive directions for each of the sequence of time slots to listen for the at least one request frame transmitted by the first transmitter;
- a second transmitter component residing on the second wireless device configured for transmitting at least one response frame to the first wireless device; and
- a digital computer system comprising a memory for storing instructions and a processor for executing the instructions for selecting a preferred set of uplink and downlink directions for further communication between the first wireless device and the second wireless device.
2. The digital computer network of claim 1, wherein a time cycle comprises a plurality N of consecutive time slots, where N equals the plurality of receive directions; and wherein the second receiver component is configured for cycling through the plurality of receive directions in each time cycle.
3. The digital computer network of claim 2, wherein each time cycle has a time-cycle boundary selected by at least one of the first wireless device and the second wireless device.
4. The digital computer network of claim 2, wherein each time cycle has a time-cycle boundary selected by at least one of the first wireless device and the second wireless device.
5. The digital computer network of claim 1, wherein the preferred set comprises a preferred transmit direction for transmitting from the second wireless device to the first wireless device, a preferred receive direction for receiving transmissions from the second wireless device to the first wireless device, and a preferred transmit direction for transmitting from the first wireless device to the second wireless device.
6. The digital computer network of claim 1, wherein the digital computer system selects the preferred set based on measurements of link quality.
7. The digital computer network of claim 1, wherein the digital computer system performs at least one of a full double sweep and a partial double sweep of all possible uplink and downlink direction pairs when selecting the preferred set.
8. The digital computer network of claim 1, wherein the preferred set comprises at least one of a set of directions having an optimal link quality and a set of directions having a link quality above a predetermined threshold.
9. The digital computer network of claim 1, wherein selecting the preferred set comprises performing at least one of a full double sweep and a partial double sweep of all possible uplink and downlink direction pairs.
10. The digital computer network of claim 1, wherein selecting the preferred set comprises selecting an uplink pair from beacon frames and selecting a downlink pair during a C-CBP direction search.
11. The digital computer network of claim 1, wherein the digital computer system is configured for maintaining a plurality of downlink direction pairs, updating a link quality indicator measurement for each of the plurality of downlink direction pairs, and updating at least one of the set of uplink and downlink directions.
12. The digital computer network of claim 1, configured for performing at least one of directional slotted ALOHA and directional cycle-based ALOHA.
13. The digital computer network of claim 1, configured for performing at least one of authentication, association, direction finding, direction tracking, communicating control frames, service period reservation, communicating command frames, communicating management frames, and communicating data frames.
14. A digital computer system, comprising:
- a transmitter configured for selecting a sequence of time slots paired with a plurality of transmit directions for transmitting at least one request frame to at least one wireless device, the at least one wireless device employing a different one of a plurality of receive directions for each of the time slots;
- a receiver configured for listening for at least one response frame transmitted by the at least one wireless device; and
- a memory for storing instructions and a processor for executing the instructions for selecting a preferred set of uplink and downlink directions for further communication with the at least one wireless device.
15. The digital computer system of claim 14, wherein selecting the sequence further comprises employing a first transmit direction for a first plurality N of the time slots, and a second transmit direction for a second plurality N of the time slots, where N equals the plurality of receive directions.
16. The digital computer system of claim 14, wherein the transmitter is configured for employing a different transmit direction for each of a plurality of time cycles when transmitting the at least one request, wherein each of a plurality of time cycles comprises a plurality N of consecutive time slots.
17. The digital computer system of claim 14, wherein each of the time slots comprises a request frame slot, a first guard interval, a response frame slot, and a second guard interval.
18. The digital computer system of claim 14, wherein the transmitter employs a set of back-off numbers corresponding to receive directions for determining back-off times for transmitting request frames.
19. The digital computer system of claim 14, wherein the transmitter employs an algorithm for selecting transmit directions and time cycles for transmitting request frames.
20. The digital computer system of claim 14, configured to perform at least one of directional slotted ALOHA and directional cycle-based ALOHA.
21. A digital computer system, comprising:
- a receiver configured for employing a different one of a plurality of receive directions for each of a sequence of time slots to listen for at least one transmitted request frame from a wireless device;
- a transmitter configured for transmitting at least one response frame in response to a received request frame; and
- a memory for storing instructions and a processor for executing the instructions for selecting a preferred set of uplink and downlink directions for further communication with the wireless device.
22. The digital computer system of claim 21, wherein a time cycle comprises a plurality N of consecutive time slots, where N equals the plurality of receive directions; and wherein listening for the at least one transmitted request frame comprises cycling through the plurality of receive directions in each time cycle.
23. The digital computer system of claim 21, wherein the request frame comprises a preferred transmit direction.
24. The digital computer system of claim 21, wherein selecting the preferred set further comprises measuring an uplink link quality indicator and transmitting the uplink link quality indicator to the wireless device.
25. A digital computer system, comprising:
- a transmitter configured for transmitting a request frame to a receiver employing a plurality of receive directions to listen for the request frame; and
- a memory for storing instructions and a processor for executing the instructions for: generating a plurality of time cycle numbers, each of the time cycle numbers being associated with one of the receive directions and having a value within a predetermined back-off window size; sequentially organizing the plurality of time cycle numbers with respect to their values for producing a sequence of time cycle numbers; and generating a sequence of time slot numbers from the sequence of time cycle numbers and the plurality of receive directions, the sequence of time slot numbers being used by the transmitter to select time slots for transmitting the request frame.
Type: Application
Filed: Dec 9, 2013
Publication Date: Jun 11, 2015
Inventor: Ismail Lakkis (San Diego, CA)
Application Number: 14/101,313