System and Method for Random Access Backoffs
A method of performing a random access procedure includes randomly selecting a backoff time from within a backoff window ranging from 0 to a specified multiple of a random access preamble unit, waiting until a time initialized with the backoff time expires, and retransmitting a random access preamble.
This application claims the benefit of U.S. Provisional Application No. 62/308,021, filed on Mar. 14, 2016, entitled “System and Method for Random Access Backoffs,” which application is hereby incorporated herein by reference.
TECHNICAL FIELDThe present invention relates generally to a system and method for digital communications, and, in particular embodiments, to a system and method for random access backoffs.
BACKGROUNDWhen a user equipment (UE) initially attaches to a network or participates in a handover between cells, a random access procedure is performed by the UE and the entity (such as an evolved NodeB (eNB), low power node (LPN), and so on) to which it is attaching in order to setup a connection with the entity.
SUMMARYExample embodiments provide a system and method for random access backoffs.
In accordance with an example embodiment, a method for performing a random access procedure is provided. The method includes randomly selecting, by a user equipment (UE), a backoff time from within a backoff window ranging from 0 to a specified multiple of a random access preamble unit, waiting, by the UE, until a time initialized with the backoff time expires, and retransmitting, by the UE, a random access preamble.
The specified multiple is one of a plurality of specified multiples, and different specified multiples are selected for random access preambles with different durations. There is a plurality of sets of specified multiples, and the specified multiple is selected from one of the plurality of sets of specified multiples in accordance with a duration of the random access preamble. The random access preamble is initially transmitted on one of a first carrier or a first band, and the random access preamble is retransmitted on one of a second carrier or a second band.
The randomly selecting the backoff time includes selecting an initial backoff time within a step of a predefined period, and selecting the backoff time within the initial backoff time. The method also includes segmenting the random access preamble into a plurality of blocks, wherein retransmitting the random access preamble comprises separately transmitting each of the plurality of blocks. The separately transmitting each of the plurality of blocks includes interleaving at least some of the plurality of blocks with an uplink data channel.
The random access preamble is transmitted in a network resource, and wherein the network resource also includes a gap inserted after the network resource so that a duration of the network resource and a gap time associated with the gap is equal to an integer multiple of a subframe duration.
In accordance with an example embodiment, a method for performing a random access procedure is provided. The method includes determining, by an evolved NodeB (eNB), a backoff parameter value in accordance with a random access preamble unit associated with a UE participating in the random access procedure, signaling, by the eNB, an indicator of the backoff parameter value, and receiving, by the eNB, a random access preamble in accordance with the backoff parameter value.
The backoff parameter value specifies a multiple of the random access preamble unit. There is a plurality of sets of specified multiples, and the specified multiple is selected from one of the plurality of sets of specified multiples in accordance with a duration of the random access preamble.
The method also includes selecting a step of a predefined period, and signaling an indicator of the step of the predefined period. The random access preamble is segmented into a plurality of blocks, and receiving the random access preamble includes separately receiving each of the plurality of blocks. The method also includes receiving an uplink data channel interleaved with at least some of the plurality of blocks.
In accordance with an example embodiment, a method for transmitting a random access preamble is provided. The method includes generating, by a UE, the random access preamble, and when a number of physical random access channel (PRACH) repetitions per attempt is larger than a threshold, segmenting, by the UE, the random access preamble into a plurality of blocks, and separately transmitting, by the UE, each of the plurality of blocks. Separately transmitting each of the plurality of blocks includes interleaving at least some of the plurality of blocks with an uplink data channel.
In accordance with an example embodiment, a non-transitory computer-readable medium storing programming for execution by at least one processor is provided. The programming including instructions to randomly select a backoff time from within a backoff window ranging from 0 to a specified multiple of a random access preamble unit, wait until a time initialized with the backoff time expires, and retransmit a random access preamble.
The specified multiple is one of a plurality of specified multiples, and the programming includes instructions to apply different specified multiples for random access preambles of different durations. There is a plurality of sets of specified multiples, and the programming includes instructions to select the specified multiple from one of the plurality of sets of specified multiples in accordance with a duration of the random access preamble. The programming includes instructions to select an initial backoff time within a step of a predefined period, and select the backoff time within the initial backoff time. The programming includes instructions to segment the random access preamble into a plurality of blocks, and separately transmit each of the plurality of blocks.
Practice of the foregoing embodiments enables the adaptation of the backoff window used in contention resolution to meet the extended preamble durations of narrow band communications systems. Fixed backoff windows cannot effectively deal with channel contention without sacrificing overall efficiency.
For a more complete understanding of the present disclosure, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
The making and using of the presently example embodiments are discussed in detail below. It should be appreciated, however, that the present disclosure provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the embodiments, and do not limit the scope of the disclosure.
The HetNet serves IoT devices, such as IoT device 220, IoT device 222, and IoT device 224, that are either mobile or immobile. The capabilities of the IoT devices may vary widely. As an example, if the IoT device is a smart device, such as a smart telephone, the IoT device may be capable of simultaneously communicating with multiple services, display multimedia, create multimedia, participate in an interactive session, serve data, and so on. As another example, if the IoT device is a sensor, such as a security sensor or a weather temperature, the IoT device may be limited to periodically report its sensory reading to a data aggregator. Regardless of the capabilities of the IoT devices, the IoT devices need to be able to establish a connection with the communications infrastructure (e.g., the HetNet in
eNBs are also commonly referred to as NodeBs, base stations, communications controllers, access points, and so on, depending on the type of the planned network infrastructure. IoT devices are also commonly referred to as user equipments (UEs), mobile stations, mobiles, terminals, users, subscribers, stations, devices, smart devices, and so on, depending on the type of the IoT devices.
While it is understood that HetNets may employ multiple eNBs capable of communicating with a number of IoT devices, only three eNBs, two LPNs, and three IoT devices are illustrated for simplicity.
As discussed previously, a random access procedure is performed by a UE when it initially attaches to a communications system or when it participates in a handover between cells. The UE participates in the random access procedure with an entity (e.g., an eNB, a LPN, and so on) of the communications system or cell. In a Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) compliant communications system, a random access procedure typically entails the UE selecting and transmitting one out of a plurality of random access preambles to the eNB (an example of an entity of the communications system as described above) and the eNB assigns network resources to the UE to allow the UE to make a connection request. If the random access procedure fails, the UE must wait a certain amount of time before the UE can try again. The amount of time that the UE waits is referred to as a backoff (BO).
The RACH backoff mechanism used in 3GPP LTE is introduced in 3GPP LTE Release-13 and is based on media access control (MAC) backoff indication (BI). Limited changes to the backoff mechanism, such as a reduction in MAC BI size from 4 bits to another value and corresponding changes to backoff range can be considered if needed and time permits. The UE randomly and uniformly chooses the backoff time from interval [0, backoff parameter value]. The interval [0, backoff parameter value] is also referred to as the backoff window. The backoff parameter value is signaled in the form of an index into a table of backoff parameter values. Table 1 shows Table 7.2-1, backoff parameter values from 3GPP TS 36.321 and Table 2 shows 3GPP LTE Physical Random Access Channel (PRACH) preamble durations.
In a narrow-band IoT (NB-IoT) ad hoc meeting and a RAN1#84 meeting, the following items were agreed upon:
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- An NB-PRACH scheme based on single-tone transmissions with 3.75 kHz subcarrier spacing is to be used in NB-IoT;
- Each transmission consists of 4 groups with each group comprising 1 cyclic prefix (CP) and 5 symbols in a symbol group; and
- 1, 2, 4, 8, 16, 32, 64, and 128 NB-PRACH repetitions are provided, with an eNB being able to configure up to 3 NB-PRACH repetitions from the 8 provided repetitions. Table 3 shows possible preamble durations based on the 8 provided repetitions.
However, these backoff parameter values and backoff time are not matched with NB-IoT preamble durations anymore. It can be seen that with repetitions, NB-IoT PRACH preamble duration is even longer than some of the backoff parameter in Table 1, hence some small values make no sense compared with longer preamble duration. For example, the backoff parameter value with toms is no use for preambles with more than one repetition.
It is noted that compared to the 3GPP LTE PRACH preamble, the NB-PRACH preamble duration can be much longer, especially in situations when a large number of repetitions are transmitted for the purpose of coverage enhancement. Furthermore, there is also a much wider variation in NB-PRACH length. In some circumstances, e.g., with larger repetition values, the NB-PRACH preamble duration is even longer than some of the backoff parameter values currently used in 3GPP LTE. Hence, some of the smaller backoff parameter values do not make practical sense when compared with larger NB-PRACH preamble durations. As an illustrative example, a backoff parameter value of 10 ms is not useful for NB-PRACH preambles with more than 1 repetition. The randomly selected backoff time does not match current NB-PRACH preamble durations. As another illustrative example, according to the 3GPP LTE backoff parameter values, if a cell load is not heavy and a backoff parameter value is selected as 10 ms, but a random access preamble has a duration of 25.6 ms (without gap time (GT)), the random access preamble will cause interference. As used herein a gap time means a time duration when no signals are transmitted. In a situation when inserted between a Physical Uplink Shared Channel (PUSCH) and a PRACH in the time domain, a gap time is the same as a guard time.
Using the current backoff mechanism, the collision probability for long preamble durations and short preamble durations differ greatly due to the wide range of preamble lengths. As an illustrative example, under the same cell load conditions and if the backoff parameter value is set to 960 ms, UEs using short preamble durations (e.g., 12.8 ms) will have many more opportunities for access with low collision probability, but UEs using long preamble durations (e.g., 819.2 ms) will have less opportunities for access with high collision probability. Additionally, due the narrow band nature of NB-IoT, long preamble durations may block and cause extra delay in NB PUSCH (NB-PUSCH) transmission. The allocation of network resources may need to be changed to reduce the blocking issue.
According to an example embodiment, the backoff parameter values are defined as multiples of random access preamble durations (random access preamble units) to align the backoff time with preamble duration. Instead of defining the backoff parameter values in time values, which results in widely varying access opportunities and collision probability with different random access preamble durations, the defining of the backoff parameter values as multiple of random access preamble units allows the access opportunities and collision probability to remain substantially constant with different random access preamble durations. Example embodiments include:
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- Example embodiment 1: The same set of backoff parameter values is used for different random access preamble durations;
- Example embodiment 2: Different sets of backoff parameter values are used for different random access preamble durations or repetitions;
- Example embodiment 3: Backoff parameter values and frequency hopping are combined to increase access opportunities and decrease collision probabilities. It is noted that frequency hopping may be performed within the same NB-PRACH band or physical resource block (PRB) or in different NB-PRACH bands or PRBs; and
- Example embodiment 4: A multi-step backoff is performed,
- Step 1—Backoff in number of a period, and
- Step 2—Random offset within a period.
Detailed discussion of these example embodiments are provided below.
According to an example embodiment, an eNB determines the backoff parameter values according to the load on corresponding random access channels. A technical standard or an operator of the communications system may define possible backoff parameter values, such as a table of possible backoff parameter values. However, an eNB selects the actual backoff parameter value(s) to signal to the UEs based on the load on the random access channels.
According to an example embodiment, network resource allocation is performed semi-statically to allocate the network resources for NB-PRACH based on random access load. Different numbers of network resources may be allocated for different NB-PRACH channels, with each random access channel being related to one NB-PRACH preamble format (e.g., duration, repetition, and so on). In order to reduce latency to the NB-PUSCH, long random access preambles may be split into multiple parts.
According to example embodiment 1, the backoff parameter values are specified as multiples of random access preamble units and the same backoff parameter values are used for different random access parameter durations. The backoff window of a UE is defined as the product of the backoff parameter value and the random access preamble unit, where the random access preamble unit is equal to the random access preamble duration for the UE. Therefore, the random access window differs for different UEs with different random access preamble durations. The use of the same backoff parameter values for different random access preamble durations is very simple with unified parameters. However, in situations with heavy loads, the latency for long random access preamble durations may be very large. The backoff parameter values may be defined by a technical standard or by an operator of the communications system. Table 4 shows an example backoff parameter value table. Table 5 shows example backoff parameter values in ms and multiples of preamble durations.
The backoff window may be used in a manner same to the backoff window in 3GPP LTE compliant communications systems, the UE randomly selects a time from within the backoff window and the UE waits the time expires before retransmitting its NB-PRACH preamble.
The backoff window may be used in a manner similar to the backoff window in 3GPP LTE compliant communications systems, the UE randomly selects a number from within the backoff window and the UE waits the number times the random access preamble unit before retransmitting its NB-PRACH preamble.
According to example embodiment 2, backoff parameter values are specified as multiples of random access preamble units and different sets of backoff parameter values are used for different random access preamble repetitions. The use of different sets of backoff preamble values for different random access preamble repetitions enable the adjustment of different backoff window sizes for different random access preamble durations. As an example, long random access preamble durations are assigned a set of backoff parameter values with small values, while short random access preamble durations are assigned a set of backoff parameter values with large values.
According to example embodiment 3, backoff parameter values are specified as multiples of random access preamble units and a combination of backoff window size and frequency hopping based on the number of random access preamble repetitions is used. As an illustrative example, a non-zero backoff window size and frequency hopping are used in situations with small numbers of random access preamble repetitions. As another illustrative example, backoff windows are not used but frequency hopping is used in situations with large numbers of random access preamble repetitions.
According to example embodiment 4, backoff parameter values are specified as multiples of random access preamble units and a multi-step backoff is performed. As an illustrative example, in a situation wherein NB-PRACH resources are periodically allocated with each period including a number of time-frequency resources allocated for random access preamble transmission, a two-step backoff includes: in a first step, backoff is performed in steps of a predefined period (the period and steps of the period are determined by the eNB or UE); and in a second step, a random offset within the period is selected (the random offset is determined by the UE). Frequency hopping can also be utilized.
In another example embodiment, it is beneficial to align NB-PRACH with 1 milli-second subframe boundary of LTE. In one alternative, different gap time can be inserted in the end of NB-PRACH. Table 7 lists example gap times that may be inserted at the end of a NB-PRACH preamble. The gap times listed in Table 7 are for illustrative purposes. The actual gap time could be different and depends on the intended cell coverage and/or the preamble duration. For example, the gap time for NB-PRACH with 128 repetitions may be 0.8 ms for 266.7 us CP and 0.2 MS for 66.7 us CP, respectively. The gap time may be used for alignment purposes, such as a 1 ms subframe boundary, for example.
In another alternative example embodiment, multiple NB-PRACH resources can be multiplexed in TDM. Each resource is dedicated to one type of NB-PRACH with the same preamble duration. Multiple allocated NB-PRACH durations are aggregated in time and followed by a gap time to align the whole PRACH resource to 1 ms subframe boundary.
In another alternative example embodiment, multiple NB-PRACH resources can be multiplexed in TDM. Each resource is dedicated to one type of NB-PRACH with the same preamble duration. Multiple allocated NB-PRACH durations are aggregated in time to align the whole PRACH resource to 1 ms subframe boundary. In this case, there is no gap time after PRACH. For example, 5 preambles with duration 6.4 ms can align with 1 ms subframe boundary.
According to an example embodiment, an eNB allocates the time-frequency resources for NB-PRACH based on the random access load. The eNB may make use of the system information block (SIB) to signal the allocations. As an illustrative example, the eNB may allocate different numbers of time-frequency resources for different random access channels, with each random access channel being related to a random access preamble format. The random access channels (i.e., the allocated time-frequency resources) may be time division multiplexed (TDM) and/or frequency division multiplexed (FDM) within one NB-PRACH band or PRB. Alternatively, the random access channels may be allocated in different NB-PRACH bands or PRBs. The load may be distributed on a random access channel basis rather than cell basis. When the load is high, more time-frequency resources may be allocated.
According to an example embodiment, the time-frequency resources allocated for random access channels are multiplexed with time-frequency resources allocated for NB-PUSCH. The multiplexing of the NB-PUSCH and the random access channels may help to reduce the latency of the NB-PUSCH cause by long NB-PRACH preambles.
According to an example embodiment, multiple bands or PRBs are used in multiplexing the NB-PRACH and the NB-PUSCH.
According to an example embodiment, long random access preambles (preambles with long durations) are split into multiple parts. Each part may be separately scheduled and transmitted. Reducing the duration of the random access preambles reduces the latency on the NB-PUSCH since the network resources are not allocated for extended amounts of time. Each of the shorter parts may utilize the backoff parameter values assigned to a whole random access preamble of the same duration as the shorter part.
Operations 1300 begin with the UE determining that the random access procedure has failed (block 1305). The random access procedure has failed if the eNB does not send a random access response to a random access preamble sent by the UE, for example. Alternatively, the random access procedure has failed if the UE receives a random access response from the eNB, but the random access response is not for the UE but another UE that sent the same random access preamble. The UE selects a backoff time from a backoff window ranging from [0, random access parameter value*random access preamble unit] (block 1310). The random access parameter value is signaled by the eNB. As an illustrative example, the eNB signals an indicator of which random access parameter value to use out of a table of random access parameter values specified by a technical standard or an operator of the communications system. The UE waits until the backoff time expires (block 1315). When the backoff time expires, the UE retransmits the random access preamble (block 1320). In some example embodiments, the random access preamble is segmented into a plurality of blocks and the UE transmits each of the plurality of blocks. In some example embodiments, the UE interleaves a PUSCH with at least some of the blocks.
In a first aspect, the present application provides a method for performing a random access procedure. The method includes randomly selecting, by a UE, a backoff time from within a backoff window ranging from 0 to a specified multiple of a random access preamble unit, waiting, by the UE, until a time initialized with the backoff time expires, and retransmitting, by the UE, a random access preamble.
According to a first embodiment of the method according to the first aspect, the specified multiple is one of a plurality of specified multiples, and different specified multiples are selected for random access preambles with different durations. According to a second embodiment of the method according to any preceding embodiment of the first aspect or the first aspect as such, there is a plurality of sets of specified multiples, and the specified multiple is selected from one of the plurality of sets of specified multiples in accordance with a duration of the random access preamble. According to a third embodiment of the method according to any preceding embodiment of the first aspect or the first aspect as such, the random access preamble is initially transmitted on one of a first carrier or a first band, and the random access preamble is retransmitted on one of a second carrier or a second band.
According to a fourth embodiment of the method according to any preceding embodiment of the first aspect or the first aspect as such, randomly selecting the backoff time includes selecting an initial backoff time within a step of a predefined period, and selecting the backoff time within the initial backoff time. According to a fifth embodiment of the method according to any preceding embodiment of the first aspect or the first aspect as such, the method also includes segmenting the random access preamble into a plurality of blocks, where retransmitting the random access preamble includes separately transmitting each of the plurality of blocks. According to a sixth embodiment of the method according to any preceding embodiment of the first aspect or the first aspect as such, separately transmitting each of the plurality of blocks includes interleaving at least some of the plurality of blocks with an uplink data channel. According to a seventh embodiment of the method according to any preceding embodiment of the first aspect or the first aspect as such, the random access preamble is transmitted in a network resource, and the network resource also includes a gap inserted after the network resource so that a duration of the network resource and a gap time associated with the gap is equal to an integer multiple of a subframe duration.
In a second aspect, the present application provides a method for transmitting a random access procedure. The method includes generating, by a UE, the random access preamble, and when a number of physical random access channel (PRACH) repetitions per attempt is larger than a threshold, segmenting, by the UE, the random access preamble into a plurality of blocks, and separately transmitting, by the UE, each of the plurality of blocks.
According to a first embodiment of the method according to the second aspect, separately transmitting each of the plurality of blocks includes interleaving at least some of the plurality of blocks with an uplink data channel.
Operations 1400 begin with the eNB determining a backoff parameter value (block 1405). The backoff parameter value is specified as a multiple of a random access preamble unit (e.g., a random access preamble duration) of the UE. As an illustrative example, the same set of backoff parameter values is used for all random access preamble units. As another illustrative example, different sets of backoff parameter values are used for different random access preamble durations. As yet another illustrative example, in addition to backoff parameter values based on random access parameter units, frequency hopping is also used. As yet another illustrative example, a multi-step backoff is used, where a period for backoff is specified and an offset within the period is either specified or is selectable by the UE. The eNB signals the backoff parameter value or an indicator thereof to the UE (block 1410). The eNB receives a random access preamble in accordance with the backoff parameter value (block 1415).
In a third aspect, the present application provides a method for performing a random access procedure. The method includes determining, by an eNB, a backoff parameter value in accordance with a random access preamble unit associated with a UE participating in the random access procedure, signaling, by the eNB, an indicator of the backoff parameter value, and receiving, by the eNB, a random access preamble in accordance with the backoff parameter value.
According to a first embodiment of the method according to the third aspect, the backoff parameter value specifies a multiple of the random access preamble unit. According to a second embodiment of the method according to any preceding embodiment of the third aspect or the third aspect as such, there is a plurality of sets of specified multiples, and the specified multiple is selected from one of the plurality of sets of specified multiples in accordance with a duration of the random access preamble. According to a third embodiment of the method according to any preceding embodiment of the third aspect or the third aspect as such, the method also includes selecting a step of a predefined period, and signaling an indicator of the step of the predefined period.
According to a fourth embodiment of the method according to any preceding embodiment of the third aspect or the third aspect as such, the random access preamble is segmented into a plurality of blocks, and receiving the random access preamble includes separately receiving each of the plurality of blocks. According to a fifth embodiment of the method according to any preceding embodiment of the third aspect or the third aspect as such, the method also includes receiving an uplink data channel interleaved with at least some of the plurality of blocks.
In order to deal with the possible collision problem caused by mismatched backoff parameter values, it is to define the backoff time as multiple times of basic time units, where the unit may equal to a preamble duration. From the RAN1 aspect, a problem is that the preamble duration (without considering GT) is not aligned with the subframe boundary of 1 ms subframe for 15 kHz subcarrier spacing and 4 ms subframe for 3.75 kHz subcarrier spacing, which may increase the scheduling complexity. According to an example embodiment, one solution is to insert gap time. Following are two examples:
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- Example A: Append a variable length of gap time after the random access preamble to align each random access preamble transmission resource with subframe boundary. As shown above in Table 3, the gaps between random access preamble durations and subframe boundary are different. There may be four kinds of gap time, e.g., {0.2 ms, 0.4 ms, 0.6 ms, 0.8 ms}, which can be used to align the random access preamble with 1 ms subframe boundary. However, some of them will result in unnecessary overhead.
- Example B: Append a predefined length of gap time after a bundle of random access preamble transmission resources to align a bundle of random access preamble transmission resources with subframe boundary. This approach is to multiplex the resources for different preamble durations by TDM; a predefined gap time (e.g., 0.2 ms) can be appended after a bundle of random access preamble transmission resources. Hence the accumulated time can be aligned with 1 ms subframe boundary.
FIG. 15 illustrates a diagram 1500 of network resources highlighting the use of a predefined gap time to align a random access preamble transmission with a 1 ms subframe boundary.
According to another example embodiment, one solution is to bundle a plurality of random access preamble transmissions without a gap time and use a resource pattern to schedule the random access preamble transmissions. In this solution, it is assumed that there is a dedicated band for random access transmissions, and eNB won't schedule NB-PUSCH in this band. Hence there is no need for GT. Multiple random access preamble transmission resources corresponding to different preamble durations are multiplexed by TDM.
Proposal 1: Consider above solutions to align the PRACH channel with NB-IoT subframe boundaries. To deal with the possible unbalanced collision probability for different PRACH preamble formats, semi-statically resource allocation for PRACH may be adopted. Firstly, a random access channel load indicator can be defined instead of current cell load. This is to say, the load is per random access channel basis. Each random access channel is related to one preamble format. When load is heavy, more resources may be allocated. Consequently, eNB can allocate different number of resources for different random access channels based on random access channel load, in which the resource allocation information may be carried via SIB.
Proposal 2: Consider semi-static resource allocation based on random access channel load to balance the collision probabilities in different random access channels for different preamble formats.
In some embodiments, the processing system 1700 is included in a network device that is accessing, or part otherwise of, a telecommunications network. In one example, the processing system 1700 is in a network-side device in a wireless or wireline telecommunications network, such as a base station, a relay station, a scheduler, a controller, a gateway, a router, an applications server, or any other device in the telecommunications network. In other embodiments, the processing system 1700 is in a user-side device accessing a wireless or wireline telecommunications network, such as a mobile station, a user equipment (UE), a personal computer (PC), a tablet, a wearable communications device (e.g., a smartwatch, etc.), or any other device adapted to access a telecommunications network.
In some embodiments, one or more of the interfaces 1710, 1712, 1714 connects the processing system 1700 to a transceiver adapted to transmit and receive signaling over the telecommunications network.
The transceiver 1800 may transmit and receive signaling over any type of communications medium. In some embodiments, the transceiver 1800 transmits and receives signaling over a wireless medium. For example, the transceiver 1800 may be a wireless transceiver adapted to communicate in accordance with a wireless telecommunications protocol, such as a cellular protocol (e.g., long-term evolution (LTE), etc.), a wireless local area network (WLAN) protocol (e.g., Wi-Fi, etc.), or any other type of wireless protocol (e.g., Bluetooth, near field communication (NFC), etc.). In such embodiments, the network-side interface 1802 comprises one or more antenna/radiating elements. For example, the network-side interface 1802 may include a single antenna, multiple separate antennas, or a multi-antenna array configured for multi-layer communication, e.g., single input multiple output (SIMO), multiple input single output (MISO), multiple input multiple output (MIMO), etc. In other embodiments, the transceiver 1600 transmits and receives signaling over a wireline medium, e.g., twisted-pair cable, coaxial cable, optical fiber, etc. Specific processing systems and/or transceivers may utilize all of the components shown, or only a subset of the components, and levels of integration may vary from device to device.
It should be appreciated that one or more steps of the embodiment methods provided herein may be performed by corresponding units or modules. For example, a signal may be transmitted by a transmitting unit or a transmitting module. A signal may be received by a receiving unit or a receiving module. A signal may be processed by a processing unit or a processing module. Other steps may be performed by a selecting unit/module, a waiting unit/module, a determining unit/module, and/or a signaling unit/module. The respective units/modules may be hardware, software, or a combination thereof. For instance, one or more of the units/modules may be an integrated circuit, such as field programmable gate arrays (FPGAs) or application-specific integrated circuits (ASICs).
Although the present disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims.
Claims
1. A method for performing a random access procedure, the method comprises:
- randomly selecting, by a user equipment (UE), a backoff time from within a backoff window ranging from 0 to a specified multiple of a random access preamble unit;
- waiting, by the UE, until a time initialized with the backoff time expires; and
- retransmitting, by the UE, a random access preamble.
2. The method of claim 1, wherein the specified multiple is one of a plurality of specified multiples, and wherein different specified multiples are selected for random access preambles with different durations.
3. The method of claim 1, wherein there is a plurality of sets of specified multiples, and wherein the specified multiple is selected from one of the plurality of sets of specified multiples in accordance with a duration of the random access preamble.
4. The method of claim 1, wherein the random access preamble is initially transmitted on one of a first carrier or a first band, and wherein the random access preamble is retransmitted on one of a second carrier or a second band.
5. The method of claim 1, wherein randomly selecting the backoff time comprises:
- selecting an initial backoff time within a step of a predefined period; and
- selecting the backoff time within the initial backoff time.
6. The method of claim 1, further comprising segmenting the random access preamble into a plurality of blocks, wherein retransmitting the random access preamble comprises separately transmitting each of the plurality of blocks.
7. The method of claim 6, wherein separately transmitting each of the plurality of blocks comprises interleaving at least some of the plurality of blocks with an uplink data channel.
8. The method of claim 1, wherein the random access preamble is transmitted in a network resource, and wherein the network resource also comprises a gap inserted after the network resource so that a duration of the network resource and a gap time associated with the gap is equal to an integer multiple of a subframe duration.
9. A method for performing a random access procedure, the method comprises:
- determining, by an evolved NodeB (eNB), a backoff parameter value in accordance with a random access preamble unit associated with a user equipment (UE) participating in the random access procedure;
- signaling, by the eNB, an indicator of the backoff parameter value; and
- receiving, by the eNB, a random access preamble in accordance with the backoff parameter value.
10. The method of claim 9, wherein the backoff parameter value specifies a multiple of the random access preamble unit.
11. The method of claim 10, wherein there is a plurality of sets of specified multiples, and wherein the specified multiple is selected from one of the plurality of sets of specified multiples in accordance with a duration of the random access preamble.
12. The method of claim 9, further comprising:
- selecting a step of a predefined period; and
- signaling an indicator of the step of the predefined period.
13. The method of claim 9, wherein the random access preamble is segmented into a plurality of blocks, and wherein receiving the random access preamble comprises separately receiving each of the plurality of blocks.
14. The method of claim 13, further comprising receiving an uplink data channel interleaved with at least some of the plurality of blocks.
15. A method for transmitting a random access preamble, the method comprising:
- generating, by a user equipment (UE), the random access preamble; and
- when a number of physical random access channel (PRACH) repetitions per attempt is larger than a threshold,
- segmenting, by the UE, the random access preamble into a plurality of blocks, and
- separately transmitting, by the UE, each of the plurality of blocks.
16. The method of claim 15, wherein separately transmitting each of the plurality of blocks comprises interleaving at least some of the plurality of blocks with an uplink data channel.
17. A non-transitory computer-readable medium storing programming for execution by at least one processor, the programming including instructions to:
- randomly select a backoff time from within a backoff window ranging from 0 to a specified multiple of a random access preamble unit;
- wait until a time initialized with the backoff time expires; and
- retransmit a random access preamble.
18. The non-transitory computer-readable medium of claim 17, wherein the specified multiple is one of a plurality of specified multiples, and wherein the programming includes instructions to select different specified multiples for random access preambles of different durations.
19. The non-transitory computer-readable medium of claim 17, wherein there is a plurality of sets of specified multiples, and wherein the programming includes instructions to select the specified multiple from one of the plurality of sets of specified multiples in accordance with a duration of the random access preamble.
20. The non-transitory computer-readable medium of claim 17, wherein the programming includes instructions to select an initial backoff time within a step of a predefined period, and select the backoff time within the initial backoff time.
21. The non-transitory computer-readable medium of claim 17, wherein the programming includes instructions to segment the random access preamble into a plurality of blocks, and separately transmit each of the plurality of blocks.
Type: Application
Filed: Mar 7, 2017
Publication Date: Sep 14, 2017
Inventors: Bin Liu (San Diego, CA), Yongbo Zeng (Beijing), Jian Wang (Hangzhou), Guorong Li (Beijing), Yu Cai (Beijing)
Application Number: 15/451,983