JP2010541381A - Method for half-duplex and full-duplex subscriber station operation in frequency division duplex systems - Google Patents

Abstract

The present invention provides a novel framing structure that can be used to smoothly evolve a time division duplex (TDD) radio communication technology into a frequency division duplex radio communication technology. The allocation start time provides a method for establishing an uplink frame start time that is an offset with respect to the downlink frame. Further provided is a method of allocating downlink and uplink resources for half-duplex and full-duplex frequency division duplex operations with appropriate rules for transmit / receive and receive / transmit time gaps. The

Description

  The present invention relates generally to communication systems, and more particularly to frequency division duplex (FDD) orthogonal frequency division multiple access (OFDMA) systems.

  Orthogonal Frequency Division Multiple Access (OFDMA) technology based on IEEE 802.16e / m and Long Term Evolution (UMTS-LTE) of universal mobile communication systems are suitable locations to become a technology of choice over 3G mobile phones Is placed in. IEEE 802.16e supports several advanced features such as scalable bandwidth, distributed and adjacent subcarrier based subchannelization methods, and multiple antenna technology. IEEE 802.16e also reflects multiple resource control functions found in 3G systems.

  One limitation of IEEE 802.16e is that it currently currently uses a single frequency carrier for both downlink and uplink, and TDD operation where the downlink and uplink are separated in time. It is limited to. Industrial implementations of this standard are currently limited to time division duplex (TDD) profiles specified by the WiMAX forum.

  FIG. 1 shows a current IEEE 802.16e TDD frame structure 100. Each frame is divided into a downlink subframe 101 and an uplink subframe 102. Downlink subframe 101 includes control overhead including preamble 111, frame control header (FCH) message 121, downlink map (DL-MAP) message 131, and uplink map (UL-MAP) message 141. Start by sending

  The preamble 111 may be used for frame synchronization, channel state estimation, received signal strength and signal-to-interference noise ratio (SINR) estimation.

  Frame control header (FCH) message 121, downlink map (DL-MAP) message 131 and uplink map (UL-MAP) message 141 describe the structure and structure of the frame.

  The time gaps denoted TTG (Transmission / Reception Transition Gap) 103 and RTG (Reception / Transmission Transition Gap) 104 are used for downlink subframes to allow transition between transmission and reception functions. It is preferably inserted between 101 and the uplink subframe 102 and at the end of each frame.

  Frequency division duplex (FDD) operation is a great benefit for operators who own a pair of spectra. However, support for FDD that can be shared is related to the operation of the base station (BS) and mobile station (MS), so a new framing structure definition that clearly specifies the timing relationship between the downlink and the uplink. Need. In this specification, the terms mobile station and subscriber station are used interchangeably.

  Some considerations must be taken into account when defining a framing structure. The first consideration is to minimize modification of the existing TDD frame structure so that undue hardware changes to the current TDD implementation are not required.

  A second consideration is support for half-duplex FDD (H-FDD) subscriber station operation. By eliminating the subscriber station duplexer, it is much easier to have a low cost terminal and develop the ASIC of the TDD terminal to the maximum FDD capability.

  A third precaution is that mobile stations supporting H-FDD and all FDD operations coexist in the same sector carrier. This ensures that the operator's investment in the H-FDD terminal is maintained as the terminal becomes more complex and evolves to maximum FDD capability.

  A fourth note is that the overhead is reduced compared to TDD. The overhead should be at least worse than in the case of TDD. There is also an improved link budget compared to TDD.

  A fifth consideration is to maximize the utilization of air interface resources by minimizing idle time.

  Ensure that the system can quickly transition from TDD to FDD operation, enable simpler H-FDD subscriber stations to be deployed, and make WiMAX based OFDMA systems compete with other systems based on other FDD technologies These functions are needed to give improvements.

  Previously proposed framing structure solutions for this problem assume a synchronized downlink and uplink frame structure, eg, increased MAP overhead, and for uplink It has several drawbacks, such as grouping subscriber stations into zones, which can lead to some degradation in the link budget.

  An exemplary embodiment of the present invention allows the start of the uplink frame to be offset with respect to the downlink frame. In the exemplary embodiment, this offset is indicated by an allocation start time (AST). The AST is preferably signaled to the SS by the base station (BS) so that the subscriber station (SS) knows both the start and end of the downlink (DL) and uplink (UL) frames.

  The present invention also takes into account rules for transition gaps from reception / transmission and transmission / reception on a per-subscriber basis relative to system-wide criteria. Furthermore, the present invention is enforced upon receiving a resource allocation message, such as a MAP message, to establish a priority for whether a mobile station is required to transmit or receive during a specific period of time. Use resource allocation rules.

  The base station may support different relevant frame periods (FD), including but not limited to 2.5 ms, 5 ms and 10 ms frames. Longer frame periods have several advantages with respect to reduced overhead and improved link budget, but shorter frames offer the potential for improved latency. The uplink transmission of an H-FDD subscriber station receives a control region in a specific downlink frame, receives downlink data in the same frame, and then transmits on the uplink according to a constrained transition gap. It can be scheduled to be done. However, if a subscriber station accidentally misses the downlink control region containing the preamble and / or resource allocation message (MAP in the case of WiMAX) during transmission on the uplink, Note that no data can be received in between and no allocation for the corresponding UL frame can be obtained.

  Full-duplex operation is possible for subscriber stations with this capability. These subscriber stations can coexist with other H-FDD capable subscriber stations and share radio resources as determined by the scheduler. Since a full duplex mobile can transmit and receive simultaneously, there is no need for a transition gap.

  Regardless of the assumed frame period, transmission in the UL is preferably capable of spanning the entire frame period. This provides the advantage of a link budget. This is because data bursts can be transmitted on fewer subchannels and more symbols, thus improving the SINR on the UL. This also allows for larger bursts to be scheduled on a given number of subchannels, thus reducing the MAC header fraction and any cyclic redundancy check (CRC) overhead. Dividing a frame into zones for half-duplex FDD operation may lead to loss in coverage for cell edge users.

  The BS scheduler (but not limited) between the known location of the UL multiple access channel (802.16 ranging channel), CQI and ACK / NACK feedback when supporting DL operations, and nominal DL and UL frames. HFDD that cannot support simultaneous DL-UL operations by taking into account multiple factors including appropriate rules for SSRTG / SSTTG gaps for switching between DL and UL assignments The utilization of both DL and UL frames for SS can be maximized. In an exemplary embodiment, any gaps that occur between consecutive DL or UL frames due to the transmission of integer-valued symbols in a single frame are minimized by appropriate selection of the OFDMA symbol cyclic prefix period for the OFDMA symbol period. May be used.

  A half-duplex SS can receive DL data, control and transmit UL data, and perform control without collision. In addition, the SS can process control messages on the DL and prepare for transmission on the UL. The HFDD SS can receive control and data in part of the DL frame, while transmitting UL control and data in part of the concurrent UL frame.

  For half-duplex FDD operation with WiMAX, maximum commonality is maintained along with existing WiMAX TDD profiles. In the exemplary embodiment, the duration of AST and uplink assignment is signaled via an existing field in UL-MAP. In an alternative exemplary embodiment, the AST and allocation period is signaled via a UCD / DCD message. These functions with maintaining uplink / downlink frame timing relationships ensure that compatibility with ASIC designs is maintained, thus reducing trading time for WiMAX FDD solutions.

FIG. 2 shows an OFDMA frame with TDD operation according to the prior art. FIG. 3 illustrates an FDD frame structure as seen from a base station according to an exemplary embodiment of the present invention. FIG. 4 shows an FDD frame structure illustrating the operation of an H-FDD subscriber station according to an exemplary embodiment of the present invention. FIG. 3 illustrates an FDD frame structure illustrating the operation of H-FDD and all FDD subscriber stations including receive / transmit and transmit / receive gaps enforced on a per-subscriber basis, according to an exemplary embodiment of the present invention. FIG. 4 illustrates an FDD frame structure illustrating resource allocation to H-FDD subscriber stations executing downlink centralized applications according to an exemplary embodiment of the present invention. FIG. 4 shows an FDD frame structure illustrating resource allocation to H-FDD subscriber stations that perform uplink centralized applications according to an exemplary embodiment of the present invention.

  FIGS. 2 through 6 illustrate exemplary embodiments of the present invention, and more particularly embodiments applicable to IEEE 802.16e / WiMAX based systems. FIG. 2 shows the frame structure 200 as seen from the base station, while FIG. 3 shows the H-FDD operation with the proposed frame structure 300, where the DL / UL offset is shown as modulo FD.

Exemplary embodiments of the present invention allow the start of uplink frames to be offset relative to the downlink by AST (Allocation Start Time). The AST is preferably informed to the SS by the base station (BS) so that the subscriber station (SS) knows both the start and end of DL and UL frames. In the exemplary system embodiment shown in FIGS. 2 and 3, the AST is defined as FD indicating that the FD is greater than the duration of the downlink (DL) or uplink (UL) frame. Any value greater than 2 ^* FD can be assumed. In this case, due to the periodic nature of the frame, the actually observed DL-FL frame offset is AST modulo FD. This maintains similar behavior for TDD systems as far as downlink and uplink resource allocation relevance is concerned via resource allocation control messages (called MAP messages in IEEE 802.16e / WiMAX). . In an alternative exemplary embodiment, the AST may not be limited to the interval described above, for example, it may be less than FD or greater than 2 ^* FD. In particular, as processing power increases in subscriber stations over time, a reduced allocation start time less than frames is possible, further reducing the latency of DL to UL resource allocation for a given terminal. It becomes possible.

  The exemplary embodiments of the present invention shown in FIGS. 3 and 4 also illustrate the receive / transmit and transmit / receive transition gaps that are preferably enforced on a per subscriber station basis relative to system-wide criteria. A transition gap for one subscriber station may be utilized to transmit data to another subscriber station or to receive data from another subscriber station. This ensures that no inefficiency is introduced into the system due to the transmit / receive transition gap.

  FIG. 5 illustrates an exemplary embodiment of a downlink centralized application for a half-duplex capable subscriber station. In the exemplary embodiment shown in FIG. 5, the subscriber station can be in all time reception mode except during the uplink control region. During the uplink control region, feedback for the downlink is preferably transmitted by the subscriber station during the transition gap between the downlink assignment and the uplink control region.

  FIG. 6 illustrates an exemplary embodiment of an uplink centralized application for a half-duplex capable subscriber station. In this exemplary embodiment, the subscriber station can be in all time transmission mode except during the downlink control region where preamble and MAP messages are transmitted by the base station.

  In addition to transition gap rules, upon receiving a resource allocation message (eg, MAP, etc.) to establish priorities as to whether a mobile station is required to transmit or receive during a specific period Preferably resource allocation rules are enforced. For example, a base station typically broadcasts system parameters such as the number of subchannels to be used in a sector periodically in the DL. These broadcast messages (BM) are preferably directed to all subscriber stations, and special priority rules are half-duplex capable to resolve conflicts between broadcast message reception and uplink transmission Must be defined for each subscriber station. In an exemplary embodiment, the base station avoids scheduling any UL transmission when scheduling the BM. This allows all half-duplex MSs to get broadcast messages while wasting part of the UL transmission bandwidth.

  In an alternative exemplary embodiment, the base station avoids wasting UL bandwidth by scheduling UL transmissions like those for normally selected H-FDD SSs. The selected SS preferably gives higher priority to the UL grant beyond any BM scheduled to overlap the UL transmission. One possible way for the SS to recover the BM lost due to collision with the UL transmission is to embed the required BM content as user traffic in the DL bearer transmission to the SS for the BS That is. Otherwise, the SS must receive the BM at one of the next broadcast reception opportunities, which may lead to some additional latency for the BM update. Although the BS scheduler can ensure that too many BM and UL assignment collisions do not occur, the above priority rules allow operation even with collisions.

  The present invention provides several advantages, in particular an OFDMA system based on IEEE 802.16e / WiMAX, and a next generation WiMAX system that will be based on the IEEE 802.16m standard. Examples of benefits include compatibility with existing TDD frame structures, smooth evolution to full FDD, resource allocation overhead for similar TDD, and reduced compared to other FDD solutions (turning to higher functionality) Reduced overhead, improved link budget, reduced header / trailer overhead fractions that translate to improved coverage.

  A further advantage of the present invention is compatibility with TDD profiles and existing hardware solutions, thus greatly reducing the trading time for FDD solutions. Furthermore, under the assumption of a 5 ms frame period, the present invention is a 2x 2 in the fixed part of the MAP overhead compared to alternative solutions such as the proposed 2.5 ms DL / UL frame. Provides a reduction. Under the assumption that the same number of bursts are scheduled within the frame period, the variable part of the MAP overhead is also reduced by a factor of two. The present invention also provides an improved uplink link budget compared to TDD.

  Furthermore, exemplary embodiments of the present invention provide support for different relevant frame periods (eg, 2.5 ms, 5 ms and 10 ms frames). As shown in the exemplary embodiment of FIG. 4, an uplink transmission of a half-duplex capable subscriber station receives a control region in a particular downlink frame and transmits downlink data in the same frame. It can be scheduled to receive and subsequently transmit on the uplink. This is illustrated for mobile station 1 (MS1), mobile station 3 (MS3) and mobile station 4 (MS4) in FIG. However, if a subscriber station accidentally misses the downlink control region containing the preamble and / or resource allocation message (MAP in the case of WiMAX) during transmission on the uplink, Note that no data can be received in the meantime.

  The exemplary embodiment shown in FIG. 4 shows that mobile station 1 (MS1) misses the DL control region of frame k + 1 due to uplink transmission in frame k, so that during frame k + 1 Indicates the case where it is impossible to be scheduled to receive downlink data. However, full-duplex operation is possible for subscriber stations with this capability. These subscriber stations can coexist with other H-FDD capable subscriber stations and share radio resources as determined by the scheduler. Since a full duplex mobile can transmit and receive simultaneously, there is no need for a transition gap. Also during these times, other subscriber stations that are not scheduled for UL transmission can listen to the DL control message and subsequently receive DL data transmission.

Regardless of the frame period, transmission in the UL preferably spans the entire frame period. This provides the advantage of a link budget. This is because data bursts can be transmitted on fewer subchannels and more symbols, thus improving the SINR on the UL. For example, consider the case where a burst is scheduled on a single subchannel that requires all available symbols (S _FDD ) in an uplink frame. In this case, the same transmission may be compared to the case of TDD that must be scheduled over S _TDD symbols as S _FDD > S _TDD . In this case, two or more subchannels must be used to schedule transmissions in TDD. In the special case of (S _FDD / S _TDD ) = 2, the signal-to-interference noise ratio is improved by 3 dB in the case of FDD compared to TDD (assuming the same in the case of two interferences). Dividing frames into zones for FDD operation (as proposed in some alternative proposals) may lead to loss in coverage for cell edge users.

Exemplary embodiments of the present invention also reduce the fraction of MAC headers and any cyclic redundancy check (CRC) overhead as it allows larger bursts to be scheduled on a given number of subchannels. . Implementation of an exemplary TDD system with 15 available symbols for uplink data and rate 1/2 QPSK (Quadrature Phase Shift Keying) transmission with hybrid automatic repeat request using PUSC In form, the overhead fraction for bursts across a single subchannel is 64 / 240-27%. On the other hand, for FDD (or H-FDD) operation with 48 available symbols, the overhead fraction is reduced to 64 / (16 ^* 48) to 8.3% overhead.

  For WiMAX FDD operation, maximum commonality is maintained with the existing WiMAX TDD profile. The allocation start time and the allocation period can be informed via the existing fields in the UL-MAP message. These functions with maintaining uplink / downlink frame timing relationships ensure that compatibility with ASIC designs is maintained, thus reducing trading time for WiMAX FDD solutions.

  Although the invention has been described with reference to specific embodiments thereof, it is not intended to be limited to the above description, but rather is limited only to the scope recited in the following claims. .

Claims (10)

A method for allocating downlink and uplink resources, comprising:
Determining a downlink start time for the downlink frame;
Determining an uplink start time for an uplink frame, wherein the uplink start time is offset from the downlink start time by an assignment start time.   Determining a time gap, wherein the time gap includes a time required for a mobile station to switch between a downlink frame and an uplink frame, and the method further includes the assignment The method of claim 1, comprising allocating resources for the mobile device such that a start time is greater than the time gap.   The method of claim 2, wherein the step of determining a time gap comprises determining a time gap for an uplink concentrated application that includes a transmit / receive transition gap.   3. The method of claim 2, wherein the step of determining a time gap includes determining a time gap for a downlink concentrated application that includes a receive / transmit transition gap.   The method of claim 2, wherein the step of determining a time gap comprises determining a time gap on a per mobile station basis.   The method of claim 1, further comprising: transmitting the allocation start time to a mobile station.   The downlink frame has a downlink period, the uplink frame has an uplink period, and the allocation start time is greater than a maximum value of the downlink period and the uplink period. The method described in 1.   The method of claim 7, wherein the allocation start time is less than twice the maximum value of the downlink period and the uplink period.   Further comprising scheduling a series of uplink resource assignments for a plurality of mobile stations communicating with the base station, wherein the series of uplink resource assignments is performed by the base station to all of the plurality of mobile stations. The method of claim 1, wherein the broadcast message is capable of being transmitted.   The method of claim 1, wherein the step of determining an uplink start time comprises determining an uplink start time utilizing a known location of an uplink control region.

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