KR20100055495A - Method for half- 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) wireless communications technology to a Frequency Division Duplex wireless communications technology. A method for establishing the start time of an uplink frame that is offset in relation to a downlink frame by an allocation start time is provided. In addition, methods of allocating downlink and uplink resources for half-duplex and full frequency division duplex operation with adequate provisions for transmit-receive and receive-transmit time gaps are also provided.

Description

METHOD FOR HALF- AND FULL-DUPLEX SUBSCRIBER STATION OPERATION IN FREQUENCY DIVISION DUPLEX SYSTEMS}

TECHNICAL FIELD The present invention generally relates to communication systems, and more particularly, to Frequency Division Duplex (FDD) Orthogonal Frequency Division Multiple Access (OFDMA) systems.

Orthogonal Frequency Division Multiple Access (OFDMA) technologies based on IEEE 802.16e / m and Universal Mobile Telecommunications System-Long Term Evolution (UMTS-LTE) are the technology of choice beyond 3G cellular. Well arranged. IEEE 802.16e supports a number of advanced capabilities such as scalable bandwidth, distributed and adjacent subcarriers based on methods of subchannelization, and multiple antenna technologies. IEEE 802.16e may mirror various resource control capabilities found in 3G systems.

One limitation of IEEE 802.16e is that a single frequency carrier is currently used for both downlink and uplink, and is currently currently limited to TDD operations where the downlink and uplink are separated by time. Industrial implementations of this standard are currently limited to the frequency division duplex (FDD) profile specified by the WiMAX Forum.

1 shows a current IEEE 802.16e TDD frame structure 100. Each frame is divided into downlink sub-frames 101 and uplink sub-frames 102. The downlink sub-frames 101 may include a preamble 111, a frame control header (FCH) message 121, a downlink map (DL-MAP) message 131, and an uplink map (UL). Begin by sending a control overhead comprising a message (141).

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

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

The time gaps indicated by the transmit-to-receive transition gap (TTG) 103 and the receive-to-transmit transition gap (RTG) 104 are the transmit and receive functions. In order to allow transitions between, it is preferred to be inserted between the downlink sub-frame 101 and the uplink sub-frame 102 and at the end of each frame, respectively.

Frequency division duplex (FDD) operation is of great interest to operators with a pair spectrum. However, the interoperable support of FDD requires a new framing structure specification that explicitly specifies downlink and uplink timing relationships, since it relates to the base station (BS) and the mobile station (MS). The terms mobile station and subscriber station are used interchangeably herein.

A number of considerations must be taken into account when defining the framing structure. The first consideration is to minimize modifications to existing TDD frame structures such that excessive hardware changes to current TDD implementations are unnecessary.

The second consideration is the support of half-duplex FDD (H-FDD) subscriber station operation. The elimination of duplexers at subscriber stations makes it much easier for TDD terminal ASICs to develop to full FDD capability with lower cost terminals.

A third consideration is the coexistence of mobile stations supporting H-FDD and full FDD operation on the same sector carrier. This will ensure that operator investments in H-FDD terminals are maintained, as terminals become more complex and develop into full FDD capability.

The fourth consideration is that overhead is reduced for TDD. At the very least, this should not be worse than the TDD case. There is also an improved link budget for TDD.

The fifth consideration is to maximize utilization of air interface resources by minimizing idle times.

These capabilities may provide improvements that allow systems to quickly migrate from TDD to FDD operation, allow simpler H-FDD subscriber stations to be deployed, and to allow WiMAX-based OFDMA systems to compete with other systems based on other FDD technologies. It is necessary to guarantee that it can.

The previously proposed framing structure solutions for this problem take a synchronized downlink and uplink frame structure, grouping subscriber stations into zones that can cause a somewhat degraded link budget for the uplink, and There are a number of disadvantages such as increased MAP overhead.

 An exemplary embodiment of the present invention allows the beginning of an uplink frame to be offset relative to the downlink frame. In an exemplary embodiment, the offset is indicated by Allocation Start Time (AST). The AST is preferably signaled to the subscriber station SS by the base station BS, so the SS knows both the downlink (DL) and uplink (UL) frame start and end times.

The invention also allows for the enforcement of transition gaps from receive-send and transmit-receive on a per subscriber basis in contrast to the overall system. In addition, the present invention utilizes a resource allocation rule that, upon receipt of resource allocation messages such as MAP messages, establishes a ranking as to whether the mobile station is required to transmit or receive for a particular period of time.

The base station may support different frame durations (FDs) of interest, which durations include, but are not limited to, 2.5 ms, 5 ms, and 10 ms frames. Longer frame durations have a number of advantages in terms of reduced overhead and improved link budget, while shorter frames provide improved latency possibilities. Uplink transmission of an H-FDD subscriber station is scheduled such that it receives a control region in a particular downlink frame, receives downlink data in the same frame, and subsequently transmits on the uplink according to the constraining transition gaps. It is possible to be. However, if a subscriber station misses a downlink control area containing a preamble and / or a resource allocation message (MAP in the case of WiMAX) when transmitting on the uplink, it will not receive data during that downlink frame. Note that neither can nor obtain an assignment for the corresponding UL frame.

Full-duplex operation is allowed for subscriber stations that possess this capability. These subscriber stations may coexist with other H-FDD capable subscriber stations and may share radio resources as determined by the subscriber. Since simultaneous transmission and reception is possible for full-duplex mobiles, there is no need for transition gaps.

Regardless of the frame duration taken, it may be desirable for transmissions on the UL to span the entire frame period. This provides a link budget advantage because data budgets can be transmitted on fewer sub-channels and more symbols, thus improving the SINR for the UL. It also allows larger bursts for a predetermined number of sub-channels to be scheduled, thus reducing the fragmentation of the MAC header and any cyclic redundancy check (CRC) overhead. Partitioning of the frame into zones for the purpose of half-duplex FDD operation can cause loss of coverage for cell-edge users.

The BS scheduler can maximize the utilization of both DL and UL frames for HFDD SSs that cannot support simultaneous DL-UL operation by considering various factors, and several factors include: UL multiple access channel (802.16 lanes) Known locations of the channel), CQI and ACK / NACK feedback in support of DL operation, and proper provision of SSRTG / SSTTG gaps for switching between DL and UL allocations during nominal DL and UL frames. Not limited). In an exemplary embodiment, any gap that occurs between successive DL or UL frames due to the transmission of integer values of symbols within a single frame is determined by appropriate selection of the OFDMA symbol periodic prefix duration with respect to the OFDMA symbol duration. Can be minimized.

A half duplex capable SS can receive DL data and control and transmit UL data and control without collision. In addition, the SS may process control messages for the DL and be ready to transmit for the UL. The HFDD SS may transmit UL control and data for a portion of the UL frames that occur simultaneously while receiving control and data for a portion of the DL frame.

For half-duplex FDD operation of WiMAX, maximum commonality is maintained with the existing WiMAX TDD profile. In an exemplary embodiment, the duration of the uplink allocation and the AST are signaled through existing fields in the UL-MAP. In an alternative exemplary embodiment, the duration of the assignment and the AST are signaled via UCD / DCD messages. Together with preservation of uplink / downlink frame timing relationships, these features ensure compatibility with ASIC designs, thus reducing the time to market WiMAX FDD solutions.

1 illustrates an OFDMA frame of a TDD operation according to the prior art.
2 is a perspective view of an FDD frame structure from a base station in accordance with an exemplary embodiment of the present invention.
3 illustrates an FDD frame structure illustrating H-FDD subscriber station operation in accordance with an exemplary embodiment of the present invention.
4 illustrates an FDD frame structure illustrating the operation of H-FDD and full FDD subscriber stations with receive-transmit and transmit-receive gaps implemented on a per-subscriber basis in accordance with an exemplary embodiment of the present invention.
FIG. 5 illustrates an FDD frame structure illustrating resource allocation for an H-FDD subscriber station executing a downlink intensive application in accordance with an exemplary embodiment of the present invention. FIG.
FIG. 6 illustrates an FDD frame structure illustrating resource allocation for an H-FDD subscriber station executing an uplink intensive application in accordance with an exemplary embodiment of the present invention. FIG.

2-6 illustrate exemplary embodiments of the present invention, in particular those applicable to IEEE 802.16e / WiMAX based systems. FIG. 2 illustrates a frame structure 200 from a base station perspectively and FIG. 3 shows an H-FDD operation to the proposed frame structure 300; DL / UL offset is shown modulo FD.

An exemplary embodiment of the present invention allows the start of an uplink frame to be offset relative to the downlink by an AST (allocation start time). The AST is preferably signaled by the base station BS to the subscriber station SS, so it knows both the DL and UL frame start and end times. In the example system embodiments shown in FIGS. 2 and 3, the AST may take any value greater than FD but less than 2 * FD, where FD is one downlink (DL) or uplink (UL). Indicates the longer duration of the frame. In this case, due to the periodic nature of the frames, the actual observed DL-UL frame offset becomes FD with the AST module. This maintains similar behavior for TDD systems as far as the relevance of downlink and uplink resource allocation via resource allocation control messages (so-called MAP messages in IEEE 802.16e / WiMAX) is concerned. In alternative exemplary embodiments, the AST may not be limited to the interval, for example, it may be less than FD or greater than 2 * FD. In particular, a reduced allocation start time less than a frame will be possible when processing power increases at the subscriber station over time and will allow the DL-UL resource allocation delay for a given terminal to be further reduced.

Exemplary embodiments of the invention shown in FIGS. 3 and 4 also show transition gaps from receive-transmit and transmit-receive that are preferably implemented on a per subscriber station basis as opposed to the overall system basis. The transition gap for one subscriber station may be utilized to send data to or receive data from another subscriber station. This ensures that no inefficiency into the system due to transmit / receive transition gaps is introduced.

5 shows an exemplary embodiment of a downlink intensive application for a half-duplex capable subscriber station. In the example embodiment shown in FIG. 5, the subscriber station may be in receive mode for all times except during the uplink control area. During the uplink control region, feedback for the downlink is preferably transmitted by the subscriber station during the transition gap between the downlink allocation and the uplink control region.

6 shows an exemplary embodiment of an uplink intensive application for a half-duplex capable subscriber station. In this exemplary embodiment, the subscriber station may be in transmission mode at all times except during the downlink control region in which preamble and MAP messages are transmitted by the base station.

In addition to enforcement of transition gaps, resource allocation rules are preferably enforced upon receipt of resource allocation messages (eg MAP) to establish a ranking as to whether the mobile station is required to be transmitted or received for a particular period of time. For example, base stations periodically broadcast system parameters, such as the number of subchannels used in a sector, over the DL. These broadcast messages (BMs) are preferably intended for all subscriber stations, and certain ranking rules should be defined for half-duplex capable subscriber stations to resolve conflicts between broadcast message reception and uplink transmission. . In an exemplary embodiment, the base station avoids scheduling any UL transmissions when scheduling BMs. In an exemplary embodiment, this allows all half duplex MSs to get broadcast messages without consuming a portion of the UL transmission bandwidth.

In an alternative exemplary embodiment, the base station avoids consuming UL bandwidth by scheduling UL transmissions, as it is generally for selected H-FDD SSs. It is desirable for the selected SSs to provide higher priority for UL grants over any BMs scheduled to overlap UL transmissions. One possible way for an SS to recover BMs missed due to a collision with UL transmissions is for the BS to insert the requested BM content in the DL bearer transmission for the SS as user traffic. Otherwise, the SS will have to receive the BM at one of the next broadcast reception opportunities, which may cause some additional delay for BM updates. The BS scheduler can ensure that many BM and UL allocation conflicts do not occur, but allow operation even if the ranking rules conflict.

The present invention provides a number of advantages in particular for OFDMA systems based on the next generation WiMAX systems and IEEE 802.16e / WiMAX that will be based on the IEEE 802.16m standard. Examples of advantages include compatibility with existing TDD frame structures, smooth deployment for full FDD, resource allocation overhead similar to TDD, and reduced overhead (transition to higher capacity) for other FDD solutions, improved links And reduced header / trailer overhead fractions that translate to budget and coverage improvements.

An additional advantage of the present invention is the compatibility of the TDD profile with existing hardware solutions, thus significantly reducing the time to market for the FDD solution. Furthermore, under the assumption of 5 ms frame duration, the present invention provides a 2x reduction of the fixed portion of MAP overhead for alternative solutions, such as the proposed 2.5 ms DL / UL frames. Under the assumption of scheduling the same number of bursts within the frame duration, the variable portion of the MAP overhead is also reduced by a factor of two. The present invention also provides an improved uplink link budget for TDD.

In addition, an exemplary embodiment of the present invention provides support of different frame durations of interest (eg, 2.5 ms, 5 ms and 10 ms frames). As shown in the exemplary embodiment of FIG. 4, the uplink transmission of a half-duplex capable subscriber station is such that it receives a control region in a specific downlink frame, receives downlink data in the same frame, and subsequently ups. It is possible to be scheduled to transmit on the link. This is shown in FIG. 4 for mobile station 1 (MS1), mobile station 3 (MS3) and mobile station 4 (MS4). However, if a subscriber station misses a downlink control area containing a preamble and / or a resource allocation message (MAP in the case of WiMAX) when transmitting on the uplink, the subscriber station does not receive data during that downlink frame. Note that you can't receive it.

The exemplary embodiment shown in FIG. 4 is scheduled such that mobile station 1 (MS1) misses the DL control region in frame k + 1 due to uplink transmission in frame k and as a result receives downlink data during frame k + 1. The case that cannot be shown is shown. However, full-duplex operation is allowed for subscriber stations possessing this capability. These subscriber stations can coexist with other H-FDD capable subscriber stations and share radio resources determined by the scheduler. Since simultaneous transmission and reception is possible for full-duplex mobiles, there is no need for transition gaps. Also, during these times, other subscriber stations that are not scheduled for UL transmission can listen to DL control messages and subsequently receive DL data transmission.

Regardless of the frame duration, the transmission on the UL preferably spans the entire frame period. This provides a link budget advantage because data bursts may have to be transmitted on more sub-channels and thus improve the SINR for the UL. For example, consider the case where a scheduling is for a single subchannel requiring all available symbols S _FDD in an uplink frame. This case may be compared to the TDD case where the same transmission should be scheduled over S _TDD symbols, where S _FDD > S _TDD . In this case, more than one sub-channel should be used to schedule transmissions in TDD. In the particular case where (S _FDD / S _TDD ) = 2, the signal-to-interference noise ratio is improved by 3 dB in the FDD case over TDD (assuming the interference is similar in the two cases). Partitioning of the frame into zones for FDD operation (as suggested in some alternative proposals) can cause loss of coverage for cell-edge users.

An exemplary embodiment of the present invention also allows larger bursts to be scheduled for a predetermined number of sub-channels, thus reducing the fragmentation of the MAC header and any periodic redundancy check (CRC) overhead. In an exemplary TDD system embodiment of 15 usable symbols for uplink data and transmission at rate 1/2 Quadrature phase-shift keying (QPSK) to hybrid automatic repeat request using PUSC, The overhead fraction for bursts is 64/240 to 27%. On the other hand, for FDD (or H-FDD) operation with 48 usable symbols, the overhead fraction is reduced from 64 / (16 * 48) to 8.3% overhead.

For the FDD operation of WiMAX, the maximum commonality is maintained with the existing WiMAX TDD profile. The allocation start time and duration of allocation may be signaled via existing fields in the UL-MAP message. Together with preservation of uplink / downlink frame timing relationships, these features ensure compatibility with ASIC designs, thus reducing the time to market WiMAX FDD solutions.

Although the invention has been described by way of specific examples, it is not intended to be limited to the above description, but is only limited to the scope set forth in the following claims.

200, 300: frame structure

Claims (10)

In a method of allocating downlink and uplink resources:
Determining a downlink start time for the downlink frame; And
Determining an uplink start time for an uplink frame, wherein
And determining the uplink start time from the downlink start time by an allocation start time offset from the downlink start time. The method of claim 1,
Determining a time gap, wherein the time gap further comprises determining the time gap, including the time required for the mobile station to switch between a downlink frame and an uplink frame;
Allocating resources for a mobile unit such that the allocation start time is greater than the time gap. The method of claim 2,
Determining the time gap includes determining a time gap for an uplink intensive application that includes a transmit-to-receive transition gap. How to allocate link resources. The method of claim 2,
Determining the time gap comprises determining a time gap for a downlink intensive application that includes a receive-transmit transition gap. The method of claim 2,
Determining the time gap comprises determining a time gap based on each mobile station. The method of claim 1,
Sending the allocation start time to a mobile station. The method of claim 1,
The downlink frame has a downlink duration, the uplink frame has an uplink duration, and the allocation start time is greater than a maximum of the downlink duration and the uplink duration; How to allocate link and uplink resources. The method of claim 7, wherein
Wherein the allocation start time is less than twice the maximum of the downlink duration and the uplink duration. The method of claim 1,
Scheduling a series of uplink resource allocations for a plurality of mobile stations in communication with a base station, wherein the series of uplink resource allocations can transmit a broadcast message to all of the plurality of mobile stations; And scheduling the series of uplink resource allocations. The method of claim 1,
Determining the uplink start time comprises determining an uplink start time using known locations of uplink control regions.

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