Filling the space-time channels in SDMA
Embodiments of the present invention provide an apparatus capable of filling space-time channels in Spatial-Division Multiple-Access (SDMA) in a Medium Access Control (MAC) protocol, comprising, a base station operable in a wireless network and adapted for uplink and downlink multi-user and multi antenna operation, the base station including a MAC scheduler to schedule transmissions using packet scheduling in the wireless network, and wherein the MAC scheduler schedules variable length packets for transmission using packet scheduling in the wireless network based on transmission times to transmit on each of M spatial channels to mobile stations operable in the wireless network by filling the M spatial channels using data packets buffered for the mobile stations operable to communicate with the base station.
This application is a continuation application of Ser. No. 10/749,293 filed Dec. 30, 2003, entitled “FILLING THE SPACE-TIME CHANNELS IN SDMA”.
BACKGROUNDSpatial-Division Multiple-Access (SDMA) is a technique that allows multiple independent transmissions between a wireless Access Point (AP) having multiple antennas and other wireless devices (mobile stations). SDMA provides a performance advantage by enabling the access point to transmit and receive signals to/from multiple stations simultaneously using different spatial channels, which increases throughput of the existing Wireless Local Area Networks (WLANs). However, a need exists for SDMA to mitigate unused channels in uplinks and downlinks.
The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which:
It will be appreciated that for simplicity and clarity of illustration, elements illustrated in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals have been repeated among the figures to indicate corresponding or analogous elements.
DETAILED DESCRIPTIONIn the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention.
In the following description and claims, the terms “coupled” and “connected,” along with their derivatives, may be used. It should be understood that these terms are not intended as synonyms for each other. Rather, in particular embodiments, “connected” may be used to indicate that two or more elements are in direct physical or electrical contact with each other. “Coupled” may mean that two or more elements are in direct physical or electrical contact. However, “coupled” may also mean that two or more elements are not in direct contact with each other, but yet still co-operate or interact with each other.
Access point 110 communicates with mobile station 120 (also referred to as “STA1”) using signal 122. Access point 110 may also communicate with mobile station 130 (also referred to as “STA2”) using signal 132, mobile station 140 (also referred to as “STA3”) using signal 142 and mobile station 150 (also referred to as “STA4”) using signal 152. Signals 122, 132, 142 and 152 are transmitted through a wireless channel in free space between access point 110 and the various mobile stations.
Access point 110 includes a processor 160 and a Radio Frequency (RF) transceiver to receive and transmit modulated signals from one or more antennas. The analog front end transceiver may be provided as a stand-alone integrated analog circuit, or alternatively, be embedded with processor 160 as a mixed-mode integrated circuit. The received modulated signals are frequency down-converted, filtered, and converted to digital signals. Access point 110 also includes a scheduler 170, a fragmentor 180 and a code rate adjuster 190 whose features are further described herein.
Thus, in the SDMA downlink and prior to time t0, access point 110 selects mobile stations that have buffered data. Scheduler 170 (see
Scheduler 170 fills M spatial channels by scheduling the traffic for M stations at any time instant, where M is a constant less than or equal to the number of antennas N at the access point. For simplicity of description and by way of example, N antennas may form M spatial channels for M stations at any time instant. The system network 100 throughput is dramatically increased when scheduler 170 fills the M spatial channels at all times. The algorithm of scheduler 170 operates to maximize the usage of the M channels, maximize the total throughput of the M channels, minimize the average bit-error rates that may be affected by the interference between spatial channels, and minimize the average latency.
In accordance with one aspect of the present invention, adaptive antenna arrays are used in conjunction with a beam forming algorithm to achieve spatial diversity within each spatial cell and implement SDMA. That is, signals output by the antennas are directionally formed by selectively energizing different antenna sensors with different signal gains so that remote terminals or mobile stations in one portion of a spatial cell may communicate with access point 110 while other remote mobile stations in a different portion of the spatial cell may communicate with the same access point, even if they are using the same tone set and code.
In another aspect of the present invention, access point 110 in the SDMA downlink first selects a group of mobile stations having buffered data, and then forms spatial channels using the adaptive antenna arrays to send data to the mobile stations. To transmit data on the spatial channels, the access point retrieves the antenna resources to form that spatial channel, with capabilities to form new channels for a waiting mobile station developed on the fly.
In particular, the access point broadcasts a clear-to-send (CTS) packet to hold the medium for a certain duration. Data packets are then sent to mobile stations 120, 130, 140 and 150 using only two spatial channels at any time instant. In the illustrated downlink example, the scheduler 170 designates two data packets, i.e., labeled Ack+Data 1 and Data 1, for mobile station 120. Scheduler 170 does not place the data packets into two spatial channels at the same time since mobile station 120 may not be equipped with multiple antennas to receive the two packets simultaneously. Therefore, scheduler 170 does not exchange the position of the latter data packet labeled Data 1 with either the data packet labeled Data 2 or the data packet labeled Ack+Data 3. Furthermore, to improve channel efficiency and increase throughput, the algorithm of scheduler 170 does not exchange the data packet labeled Data 1 with the data packet labeled Data 4.
The access point broadcasts the schedule packet in order to both announce the transmission opportunities (or intervals) and hold the medium for a certain duration. After the broadcasted schedule is received by mobile stations 120, 130, 140 and 150, the addressed stations respond by sending their data packets within the specified intervals. Mobile station 120 (STA1) is assigned two time intervals and that station sends two packets in the first interval and one packet in the second interval. Access point 110 may broadcast the schedule using an omni-directional antenna, since the schedule is directed collectively to mobile stations 120, 130, 140 and 150, and there are only two spatial channels available at each time instant.
By now it should be apparent that a Medium Access Control (MAC) protocol may be used to enhance the efficiency of SDMA systems in accordance with features of the present invention, such features including fragmentation, data traffic scheduling, adding error rate control bits and retrieving antenna resources to form spatial channels developed on the fly.
While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
Claims
1. A apparatus capable of filling space-time channels in Spatial-Division Multiple-Access (SDMA) in a Medium Access Control (MAC) protocol, comprising:
- a base station operable in a wireless network and adapted for uplink and downlink muliti-user and multi antenna operation, said base station including a MAC scheduler to schedule transmissions using packet scheduling in said wireless network; and
- wherein said MAC scheduler schedules variable length packets for transmission using packet scheduling in said wireless network based on transmission times to transmit on each of M spatial channels to mobile stations operable in said wireless network by filling the M spatial channels using data packets buffered for said mobile stations operable to communicate with said base station.
2. The apparatus of claim 1, where M is a constant less than or equal to a number of antennas at the access point.
3. The apparatus of claim 1, further including adaptive antenna arrays used in conjunction with a beam forming algorithm to achieve spatial diversity and implementing Spatial-Division Multiple-Access (SDMA), wherein the adaptive antenna array changes beam weights based on the schedule.
4. The apparatus of claim 1, wherein the scheduler in a downlink provides a schedule of transmission intervals for different mobile stations.
5. The apparatus of claim 1, wherein the schedule accounts for traffic information to the mobile stations based on packet size.
6. The device of claim 1, wherein the schedule accounts for traffic information to the mobile stations based on queue size.
7. The apparatus of claim 1, wherein the schedule accounts for traffic information to the mobile stations based on priority.
8. The apparatus of claim 1, wherein the access point sends multiple schedules in a protected time interval to the mobile stations.
9. The apparatus of claim 8, wherein a first schedule of the multiple schedules is sent to a first mobile station and a second schedule is sent to a second mobile station.
10. A method to fill space-time channels in Spatial-Division Multiple-Access (SDMA) in a Medium Access Control (MAC) protocol, comprising:
- using a base station operable in a wireless network and adapted for uplink and downlink muliti-user and multi antenna operation, said base station including a MAC scheduler to schedule transmissions using packet scheduling in said wireless network; and
- wherein said MAC scheduler schedules variable length packets for transmission using packet scheduling in said wireless network based on transmission times to transmit on each of M spatial channels to mobile stations operable in said wireless network by filling the M spatial channels using data packets buffered for said mobile stations operable to communicate with said base station.
11. The method of claim 10, where M is a constant less than or equal to a number of antennas at the access point.
12. The method of claim 10, further including retrieving antenna resources in the access point to form spatial channels developed on the fly for a waiting mobile station.
13. The method of claim 10, wherein a channel is accessed by the access point sending a Clear-To-Send (CTS) frame that broadcasts a protected time interval, and wherein the protected time interval is announced by the access point such that no mobile station contends for the medium during that time interval.
14. The Method of claim 13, wherein the time interval length may be equal to the length of a buffered packet.
Type: Application
Filed: Sep 10, 2009
Publication Date: Jan 7, 2010
Inventors: Xintian E. Lin (Palo Alto, CA), Qinghua Li (Sunnyvale, CA)
Application Number: 12/584,780
International Classification: H04J 3/00 (20060101);