CN101189816A - Method and apparatus for reducing round-trip delay and overhead in a communication system - Google Patents

Abstract

During operation radio frames are divided into a plurality of subframes. Data is transmitted over the radio frames within a plurality of subframes, and having a frame duration selected from two or more possible frame durations.

Description

Method and apparatus for reducing round-trip delay and overhead in a communication system

related application

This application claims priority to US Provisional Application Serial No. 60/666494, filed March 30, 2005.

technical field

The present invention relates generally to communication systems, and in particular, to a method and apparatus for reducing round-trip delay and overhead in a communication system.

Background technique

A key requirement for the development of wireless broadband systems, such as in the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), is to reduce latency in order to improve user experience. From a link layer perspective, the key contributor to latency is the round-trip delay between packet transmission and packet receipt acknowledgment. This round-trip delay is typically defined as a number of frames, where a frame is the length of time to execute the schedule. The round-trip delay itself determines the overall automatic repeat request (ARQ) design, including design parameters such as the delay between first and subsequent packet transmissions, or the number of hybrid ARQ channels (instances). Therefore, latency reduction focused on defining an optimal frame duration is critical to develop an improved user experience in future communication systems. Such systems include Enhanced Universal Terrestrial Radio Access (UTRA) and Evolved Universal Terrestrial Radio Access Network (UTRAN) (also known as EUTRA and EUTRAN) in 3GPP, and communication systems in other organizations that produce technical specifications ("Phase 2" in 3GPP2, and the evolution of IEEE 802.11, 802.16, 802.20, and 802.22).

Unfortunately, there is no optimal single frame duration for different traffic types that require different quality of service (QoS) characteristics or provide different packet sizes. This is especially true when considering control channels and pilot overhead in frames. For example, if the absolute control channel overhead per user per resource allocation is constant, and a single user is allocated per frame, a frame duration of 0.5ms will be roughly four times smaller in effectiveness than a frame duration of 2ms . Furthermore, different manufacturers or operators may prefer different frame durations, making it difficult to develop industry-standard or compliant devices. Therefore, there is a need for an improved method for reducing round-trip delay and overhead in a communication system.

Description of drawings

Figure 1 is a block diagram of a communication system.

Fig. 2 is a block diagram of circuits for performing uplink and downlink transmissions.

Fig. 3 is a block diagram of a radio frame.

Figure 4 shows a sequence of consecutive short frames.

Figure 5 shows a continuous long frame sequence.

Figure 6 shows a table of 10ms radio frames and subframes of approximately 0.5ms, 0.55556ms, 0.625ms and 0.67ms.

Fig. 7 shows an example for the third data column of Table 1, which has a subframe of 0.5ms, and each long frame (3ms) has 6 subframes.

Figure 8 shows two examples of radio frames based on a combination of 2ms long frames and 0.5ms short frames.

Fig. 9 shows a subframe comprising j = 10 OFDM symbols each with a cyclic prefix 901 of 5.56 μs, which can be used for unicast transmission.

Figure 10 shows a "broadcast" subframe comprising j = 9 symbols each with a cyclic prefix 1001 of 11.11 μs, which can be used for broadcast transmissions.

Figure 11 shows a table with an example of three subframe types.

Figure 12 shows a long frame consisting of either all broadcast subframes or all regular (unicast) subframes.

FIG. 13 shows a short frame composed of a regular subframe or a broadcast subframe and one or more broadcast type short frames.

Fig. 14 shows an example of radio frame overhead.

Figure 15 shows an alternate radio frame structure of arbitrary size, where the synchronization and control (S+C) region is not part of the radio frame, but part of a larger hierarchical frame structure composed of radio frames, the larger hierarchical The frame structure consists of radio frames of the (S+C) region transmitted every j radio frames.

Figures 16 and 17 illustrate a hierarchical frame structure, where a superframe is defined to consist of n+1 radio frames.

FIG. 18 shows an uplink subframe having the same configuration as a downlink subframe.

FIG. 19 to FIG. 21 show a 2ms long frame composed of 0.5ms subframes, which has a frame type of long RACH, data (Data) or composite (Composite).

Detailed ways

In response to the needs mentioned above, a method and apparatus for reducing round-trip latency are provided herein. During operation, a radio frame is divided into subframes. Data is transmitted on the radio frame in a plurality of subframes and has a frame duration selected from two or more feasible frame durations.

The present invention includes a method for reducing round-trip delay in a communication system. The method comprises the step of receiving data to be transmitted on a radio frame, wherein the radio frame comprises a plurality of subframes. The frame duration is selected from two or more feasible frame durations, where a frame is substantially equal to a number of subframes. Data is arranged in the plurality of subframes to generate a plurality of data subframes, and the frame with the plurality of data subframes is transmitted on the radio frame.

Furthermore, the invention comprises a method comprising the step of receiving data to be transmitted to the first user on a radio frame, wherein the radio frame comprises a plurality of subframes. A frame duration is selected for the first user from two or more possible frame durations, where a frame is substantially equal to a number of subframes. Data for the first user is arranged in the plurality of subframes to generate a plurality of data subframes, and the frame with the plurality of data subframes is then transmitted to the first user on the radio frame. Second data to be transmitted to a second user on the radio frame is received. A second frame duration is selected for the second user from the two or more possible frame durations, wherein the second frame is substantially equal to a plurality of subframes. Second data for a second user is arranged in said plurality of subframes to generate a second plurality of data subframes, and a second frame having said second plurality of data subframes is transmitted on said radio frame to the second user.

The invention includes a method for communicating data in a communication system. The method comprises the step of receiving data to be transmitted on a radio frame, wherein the radio frame comprises a plurality of subframes. A frame length is selected to include a plurality of subframes, and a subframe type is selected from two or more subframe types for the plurality of subframes. The data is arranged in the plurality of subframes to generate a plurality of data subframes, and the frame having the plurality of data subframes and the subframe type is transmitted on the radio frame.

The invention includes a method for communicating data in a communication system. The method comprises the step of receiving data to be transmitted on a radio frame, wherein the radio frame comprises a plurality of subframes. A frame is selected, where the frame is substantially equal to a number of subframes. The data is placed in the plurality of subframes to generate a plurality of data subframes, and a common pilot is placed in each of the plurality of subframes. The frame having the plurality of data subframes is transmitted on the radio frame.

The invention includes a method for communicating data in a communication system. The method comprises the steps of determining a system bandwidth from among two or more system bandwidths and receiving data to be transmitted on radio frames and said system bandwidth. The radio frame includes a plurality of subframes, and the radio frame duration and subframe duration are based on the system bandwidth. A frame is selected, where the frame is substantially equal to a number of subframes. The data is arranged in the plurality of subframes to generate a plurality of data subframes, and the frame having the plurality of data subframes and the subframe type is transmitted on the radio frame.

A method for communicating data in a communication system. The method includes the steps of determining a carrier bandwidth and receiving data to be transmitted on a radio frame, wherein the radio frame includes a plurality of subframes. A frame is selected, wherein the frame is substantially equal to a plurality of subframes, and each subframe comprises resource elements, wherein the resource elements comprise a plurality of subcarriers such that the carrier bandwidth is divided into a plurality of resource elements. The data is arranged in the plurality of subframes to generate a plurality of data subframes, and the frame having the plurality of data subframes and the subframe type is transmitted on the radio frame.

Turning now to the drawings, wherein like reference numerals represent like elements, FIG. 1 is a block diagram of a communication system 100 . The communication system 100 includes a plurality of cells 105 (only one shown) each having a base transceiver station (BTS, or base station) 104 that communicates with a plurality of remote or mobile units 101-103. In a preferred embodiment of the invention, the communication system 100 utilizes a next-generation Orthogonal Frequency Division Multiplexing (OFDM) or multicarrier-based architecture, such as OFDM with or without a cyclic prefix or guard interval (e.g., with a cyclic prefix or Traditional OFDM with guard interval, OFDM with pulse shaping but without cyclic prefix or guard interval (OFDM/OQAM with IOTA (Isotropic Orthogonal Transform Algorithm) prototype filter)), or with or without cyclic prefix or Single carrier for guard intervals (eg, IFDMA, DFT-Spread-OFDM), etc. Data transmissions may be downlink transmissions or uplink transmissions. Transmission schemes may include Adaptive Modulation and Coding (AMC). The architecture may also include the use of spread spectrum techniques such as Multi-Carrier CDMA (MC-CDMA), Multi-Carrier Direct-Sequence CDMA (MC-DS-CDMA), Orthogonal Frequency Division and Code Division with one-dimensional or two-dimensional spreading Multiplexing (OFCDM), or may be based on simpler time division and/or frequency division multiplexing/multiple access techniques, or a combination of the various techniques. However, in alternative embodiments, communication system 100 may utilize other wideband cellular communication system protocols such as, but not limited to, TDMA or direct sequence CDMA.

In addition to OFDM, communication system 100 utilizes Adaptive Modulation and Coding (AMC). With AMC, the modulation and coding format of the transport data stream to a particular receiver becomes primarily matched (at the receiver) to the current received signal quality for the particular frame being transmitted. Modulation and coding schemes can be varied from frame to frame to facilitate tracking of channel quality changes that occur in mobile communication systems. Thus, high quality streams are typically assigned higher modulation rates and/or higher channel coding rates, with modulation levels and/or coding rates decreasing as quality decreases. For those receivers experiencing high quality, modulation schemes such as 16 QAM, 64 QAM or 256QAM are utilized, while for those experiencing low quality, modulation schemes such as BPSK or QPSK are utilized.

For each modulation scheme, multiple coding rates can be utilized to provide finer AMC granularity for closer matching between quality and transmitted signal characteristics (e.g., for QPSK, R=1/4, 1/ 2 and 3/4; and for 16 QAM, R = 2/3, etc.). It should be noted that AMC can be performed in the time dimension (eg, modulation/coding update every N _t OFDM symbol periods) or in the frequency dimension (eg, modulation/coding update every N _sc subcarriers) or by a combination of both.

For reasons such as channel quality measurement delays or errors or channel quality reporting delays, the selected modulation and coding may primarily only match the current received signal quality. This delay is typically caused by the round-trip delay between packet transmission and packet receipt acknowledgment.

To reduce latency, a Radio Frame (RAF) and subframe are defined, and the RAF is divided into a number (in the preferred embodiment, an integer number) of subframes. In a radio frame, where a frame is constructed from an integer number of subframes for data transmission, two or more frame durations are available (eg, a first frame duration of one subframe, and a second frame duration of three subframes).

For example, a 10 ms core radio frame structure from UTRA may be defined, each radio frame having N _rf subframes (e.g. N _rf =20 subframes of T _sf =0.5 ms, where T _sf = duration of one subframe) . For OFDM transmission, a subframe includes an integer number of P OFDM symbol intervals (for example, for a symbol of T _sn =50 μs, P=10, where T _sn =the duration of one OFDM symbol), and one or Multiple subframe types (eg, regular or broadcast).

As will be appreciated by those of ordinary skill in the art, frames are associated with scheduling data transmissions. A frame can be defined as a 'schedulable' resource or schedulable unit, where the frame has an associated (possibly uniquely associated) control structure that controls the use of the resource (ie allocation to users etc.). For example, when users are to be scheduled on a frame, the resource allocation message corresponding to the frame will provide resources in the frame (eg, for an OFDM system, a number of modulation symbols per subcarrier on one OFDM symbol) for transmission. Acknowledgments for data transmissions on frames will be returned, and new data or data retransmissions can be scheduled on future frames. Since not all resources in a frame are allocated in resource allocations, such as in OFDM systems, resource allocations may not span all available bandwidth and/or time resources in a frame.

Depending on the type of traffic being served, different frame durations can be used to reduce latency and overhead. For example, if a first transmission and a retransmission are required to reliably receive a Voice over Internet Protocol (VoIP) data packet, and the retransmission can only occur after a delay of one frame, then in a 0.5ms frame instead of a 0.2ms frame Allocating resources reduces the latency of reliable reception from 6ms (transmission, idle frame, retransmission) to 1.5ms. In another example, providing resource allocation that fits user packets without fragmentation, such as lms frames instead of 0.5ms frames, can reduce overhead, such as control and acknowledgment signaling for multiple fragments of the packet.

Other names reflecting sets of resources, such as consecutive OFDM symbols, may be used instead of subframe, frame and radio frame. For example, the term "slot" may be used for "subframe", or "transmission time interval (TTI)" may be used for "frame" or "frame duration". Furthermore, frames can be considered quantities specific to user transmissions (such as TTIs associated with users and data streams), and thus frames do not need to be synchronized or aligned between users or even between transmissions from the same user (e.g., A subframe may contain parts of two data transmissions from the user, the first transmission in a frame of one subframe and the second transmission in a frame of four subframes). Of course, it is advantageous to limit transmissions to the same user or to multiple users to frames with synchronization or alignment, such as in sequences of frames that divide time into 0.5 ms or 2 ms, and all resource allocations must be within these frames in the middle. As noted above, a radio frame may represent a subframe or a collection of frames of different sizes, or a collection of resources, such as consecutive OFDM or DFT-SOFDM symbols, exceeding the number of symbols in a subframe, where in a subframe , each symbol consists of a certain number of subcarriers depending on the carrier bandwidth.

Furthermore, the radio frame structure can be used to define common control channels (such as broadcast channel, paging channel, synchronization channel and/or indicator channel) for downlink (DL) transmission in such a way that they are time-division multiplexed into sub- A sequence of frames, which can simplify processing or increase battery life at the user equipment (remote unit). Similarly, for uplink (UL) transmissions, the radio frame structure can additionally be used to define contention channels (e.g. Random Access Channel (RACH)), control including pilot times for multiplex operation with shared data channels channel.

2 is a block circuit diagram 200 for base station 104 or mobile stations 101-103 to perform uplink and downlink transmissions. As shown, circuit 200 includes logic circuit 201 , transmit circuit 202 and receive circuit 203 . Logic circuit 200 preferably includes a microprocessor controller such as, but not limited to, a Freescale PowerPC microprocessor. The transmission and reception circuits 202 to 203 are common circuits known in the art for communicating using well-known network protocols, and serve as means for transmitting and receiving messages. For example, transmitter 202 and receiver 203 are preferably well-known transmitters and receivers using 3GPP network protocols. Other possible transmitters and receivers include, but are not limited to, transceivers utilizing Bluetooth, IEEE 802.16, or HyperLAN protocols.

During operation, the transmitter 203 and receiver 204 transmit and receive data frames as discussed above, as well as control information. More specifically, data transmission occurs by receiving data to be transmitted on radio frames. A radio frame (shown in FIG. 3 ) comprises a plurality of subframes 300 (only one is marked), wherein the duration of the subframe 301 is substantially constant, and the duration of the radio frame 300 is constant. For example, a radio frame comprises m=20 subframes 300 of duration 0.5 ms, consisting of j=10 symbols. During transmission, the logic circuit 201 selects a frame duration from two or more frame durations, where a frame duration is basically a subframe duration multiplied by a number. Based on the frame duration, the number of subframes is organized in a frame, and data is placed in a subframe. Transmission occurs by transmitter 202 transmitting a frame 300 having the number of subframes on a radio frame.

As mentioned earlier, data transmissions may be downlink transmissions or uplink transmissions. The transmission scheme can be OFDM with or without cyclic prefix or guard interval (e.g. conventional OFDM with cyclic prefix or guard interval, OFDM with pulse shaping but without cyclic prefix or guard interval (with IOTA (Isotropic Positive Alternating Algorithms) OFDM/OQAM with prototype filters), or single carrier with or without cyclic prefix or guard interval (eg, IFDMA, DFT-Spread-OFDM), CDM, etc.

frame duration

There are two or more frame durations. If two frame durations are defined, they can be specified as short or long, where the short frame duration includes fewer subframes than the long frame duration. FIG. 4 shows a continuous short frame sequence 401 (short frame multiplexing), while FIG. 5 shows a continuous long frame sequence 501 (long frame multiplexing). Time can be divided into a sequence of subframes, the subframes are organized in frames of two or more durations, and the frame durations can vary between consecutive frames. A subframe of a frame has a subframe type, typically two or more subframe types. Each short frame and long frame is a schedulable unit consisting of ns(n) subframes. In the examples of Figures 4 and 5, the subframes have a duration of 0.5 ms and 10 symbols, ns=1 for the short frame 401 and n=6 (3 ms) for the long frame 501, although other value. A radio frame need not be defined, or if a radio frame is defined, a frame (eg, a short frame or a long frame) may span more than one radio frame. As an example, common pilots or common reference symbols or common reference signals are time division multiplexed (TDM) on the first symbol of each subframe, and control symbols are TDM on the first symbol of each frame (other forms of multiplexing operations such as FDM, CDM, and combining). Pilot symbols and resource allocation control configuration will be discussed in later chapters, and the purpose here is to show that the control overhead of a long frame can be smaller than that of a short frame.

A radio frame (radio frame) may comprise a short frame 401, a long frame 501, or some combination of short and long frames. A single user can have short and long frames in a radio frame, or can be limited to one frame duration. The frames of multiple users may be synchronized or aligned, or may be asynchronous or non-aligned. In general, a frame (eg, a short frame or a long frame) may span more than one radio frame. Several different long frame configurations are shown in Table 1 of FIG. 6 for radio frames of 10 ms and subframes of approximately 0.5 ms, 0.55556 ms, 0.625 ms and 0.67 ms. In this example, the short frame duration is one subframe, while the long frame duration varies. For each configuration, the maximum number of long frames per radio frame, and the minimum number of short frames per radio frame are shown. An optional radio frame overhead (in subframes) is assumed (eg for the aforementioned common control channel), which will be discussed in the "Radio Frame Overhead Multiplexing" section. However, radio frames and other overhead can also be multiplexed within frames (data subframes). For purposes of simplicity and flexibility, it is preferred, but not required, that the radio frame overhead is an integer number of subframes.

Fig. 7 shows an example of the third data column in Table 1, each long frame (3ms) has 6 subframes of 0.5ms. In the example of Figure 7, a radio frame starts with two synchronization and control subframes (radio frame overhead) 701, followed by 18 short frames 702 (only one is marked) or 3 long frames 703 (only one is marked). One), where each long frame consists of 6 subframes. An additional (optional) parameter in this example is the minimum number of bursts per radio frame (last row of the table). This parameter determines whether radio frames must contain certain short frames. By setting the minimum number of short frames per radio frame to zero, radio frames are allowed to be completely filled with long frames instead of short frames. Since the minimum number of short frames per radio frame is zero, mixing of short and long frames in a radio frame can be prohibited (normally allowed).

Alternatively, Table 1 also shows that each long frame (2ms) has 4 table entries of 0.5ms subframes. Figure 8 shows two examples of radio frames based on a combination of 2ms long frames and 0.5ms short frames. Feasible starting positions of long frames may be restricted to known positions in the radio frame.

Reasons for choosing a specific frame duration

As an example, the frame duration may be selected based in part on the following factors:

• Specific hardware that has a preference for frame duration, including capabilities of the user equipment.

· Operator or manufacturer preferences, which may include (among other factors) deployment preferences or available spectrum and adjacency with other deployed wireless systems

· Channel bandwidth (such as 1.25MHz or 10MHz),

• User conditions from one or more users, where user conditions may be speed (Doppler), radio channel conditions, user's location in the cell (eg cell edge) or other user conditions.

• User traffic characteristics of one or more users, such as delay requirements, packet size, error rate, allowable number of retransmissions, etc.

• The frame duration may be selected based in part on minimizing overhead for one or more users. The overhead may be control overhead, segmentation overhead (eg, CRC), or other overhead.

The number of users to be scheduled in the frame

• Radio network status, including system "load" and number of users in each cell.

·Backward compatibility with legacy systems

Frequency and modulation division of the carrier and assigned service type: the entire carrier can be divided into two or more bands of different sizes, with different modulation types used in each band (for example, the carrier bandwidth is divided into CDMA or single carrier or spread spectrum OFDM bands and multi-carrier OFDM bands), whereby for the type of traffic assigned or scheduled in each band (e.g. VoIP in the CDMA band and web browsing in the other OFDM bands), the different frame sizes are better or (approximately) optimal

As an example, consider selecting a frame duration for a single user between a short frame (eg, a frame duration less than a maximum number of subframes) and a long frame (eg, a frame duration greater than a minimum number of subframes). Short frames can be chosen for lowest latency, smallest packet, medium Doppler, large bandwidth, or other reasons. Long frames can be chosen for lower overhead, low latency, larger packets, low or high Doppler, cell edge, small bandwidth, multi-user scheduling, frequency selective scheduling, or other reasons. However, in general no hard rules need to be applied, so any delay, packet size, bandwidth, Doppler, location, scheduling method, etc. can be used in any frame duration (short or long). For example, the subframe duration may correspond to a minimum downlink frame or TTI. Multiple subframes concatenated into longer frames or TTIs may, for example, provide support for lower data rates and QoS optimization.

The frame duration may be selected based on any of a number of granularities. Frame duration or TTI can be a semi-static or dynamic transport channel attribute. In this way, the frame duration or TTI can be determined frame by frame (and thus dynamically) or semi-statically. In the dynamic case, the network (Node B) will signal the frame duration either explicitly (eg with L1 bit) or implicitly (eg by indicating modulation and coding rate and transport block size). In the case of a semi-static frame duration or TTI, the frame duration or TTI can be set through signaling at a higher layer (eg, L3). Granularities include, but are not limited to, frame by frame, within a radio frame, between radio frames, every multiple of radio frames (10, 20, 100, etc.), every number of ms or s (e.g., 115ms, 1s, etc.), When switching, when the system is registered, when the system is deployed, when an L3 message is received, etc. Granularity may be named "static," "semi-static," "semi-dynamic," "dynamic," or other terms. The frame duration or TTI may also be triggered when any of the above "selection" characteristics change, or for any other reason.

subframe type

In both downlink and uplink, there is at least one type of subframe, and typically, for downlink (and sometimes for uplink), there are usually two or more types of subframes (each frames have substantially the same duration). For example, the types could be "regular" and "broadcast" (for downlink transmissions), or types A, B, and C, and so on. In this case, the data transfer procedure is extended to include:

receiving data to be transmitted on a radio frame, wherein the radio frame comprises a plurality of subframes, wherein the duration of the subframes is substantially constant, and the duration of the radio frame is constant;

Select a frame duration from two or more frame durations, where a frame duration is essentially a subframe duration multiplied by a number;

Organize the number of subframes into the frame based on the frame duration

• Selection of a subframe type, where the selected subframe type specifies the amount of data that can be accommodated in the subframe

Place data in a subframe with the subframe type

• A frame with that number of subframes is transmitted on a radio frame.

As noted, all subframes in a frame are of the same type, although in general subframe types may be mixed within a frame.

The subframe type can be distinguished by transmission parameters. For OFDM transmissions, this may include guard interval duration, subcarrier spacing, number of subcarriers or FFT size. In a preferred embodiment, the subframe type can be distinguished by the guard interval (or cyclic prefix) of the transmission. In examples, such transmissions are referred to as OFDM transmissions, although guard intervals may also be applied to single carrier (eg, IFDMA) or spread spectrum (eg, CDMA) signals as is known in the art. Longer guard intervals can be used to deploy larger cells, broadcast or multicast transmissions, release synchronization requirements, or uplink transmissions.

As an example, consider an OFDM system with 22.5 kHz subcarrier spacing and a symbol duration of 44.44 μs (non-spread). Figure 9 shows a subcarrier 900 comprising j = 10 OFDM symbols each with a cyclic prefix of 5.56 μs, which can be used for unicast transmission. Figure 10 shows a "broadcast" subframe 1000 comprising j = 9 symbols each with a cyclic prefix 1001 of 11.11 μs, which may be used for broadcast transmissions. In the figure, the use of symbols in a subframe is not shown (eg, data, pilot, control or other functions). It is evident that the cyclic prefix 1001 for broadcast subframes is larger (in time) than the cyclic prefix 901 for unicast (not multicast or broadcast) subframes. Therefore, the frame can be identified as a short frame or a long frame by the length of the cyclic prefix of the frame. Of course, a subframe with a longer CP can be used for unicast, while a subframe with a shorter CP can be used for broadcast, so a name such as subframe type A or B is appropriate.

An example of three subframe types for 22.5 kHz subcarrier spacing and subframes of approximately 0.5, 0.5556, 0.625 and 0.6667 ms is provided in Table 2 shown in FIG. 11 . Three cyclic prefix durations (for subframe types A, B and C) are shown for each subframe duration. Other subcarrier spacings may also be defined, such as, but not limited to, 7-8 kHz, 12-13 kHz, 15 kHz, 17-18 kHz. Also, in a subframe, all symbols may not have the same symbol duration due to different guard duration (cyclic prefix) or different subcarrier spacing or FFT size.

The OFDM numerical nomenclature scheme used is exemplary only, and many others are possible. For example, Table 3 shown in Figure 11 uses 25kHz subcarrier spacing. As shown in this example (e.g., 0.5 ms subframe, 5.45 μs guard interval), there can be non-uniform guard interval durations in a subframe, such as when the required number of symbols does not divide the number of samples per subframe . In this case the table entry represents the average cyclic prefix of the subframe symbols. An example of how to modify the cyclic prefix of each subframe symbol is shown in the "Scalable Bandwidth" section.

A long frame can consist entirely of broadcast subframes, or entirely of regular (unicast) subframes (see Figure 12), or a combination of regular and broadcast subframes. One or more long frames of broadcast type may appear in a radio frame. A short frame may also consist of regular or broadcast subframes, and one or more broadcast type short frames may appear in a radio frame (see FIG. 13 ). Broadcast frames can be grouped with other broadcast frames to improve channel estimation for unicast and non-unicast data (see "Pilot symbols" section; common pilots from adjacent subframes can be used), and/or can Interleave non-broadcast frames between broadcast frames for time interleaving. Although not shown, at least one additional subframe type may be of type 'blank'. Blank subframes may be empty, or contain fixed or pseudo-randomly generated payloads. Blank subframes may be used to avoid interference, measure interference, or when there is no data present in frames of radio frames. Other subframe types may also be defined.

Radio frame auxiliary function multiplexing

A portion of the radio frame may be reserved for auxiliary functions. Ancillary functions may include radio frame control (including common control structures), synchronization fields or sequences, indicator signaling responses to activity on complementary radio channels (such as FDD carriers versus accompanying frequencies), or other types of overhead.

In Fig. 14, an example of radio frame overhead called "Synchronization and Control Region" is illustrated. In this example, the overhead is 2 subframes time multiplexed in a radio frame of 20 subframes. Other forms of multiplexing synchronization and control in subframes are also possible. Synchronization and control regions can include multiple types of synchronization symbols (including cell-specific Cell Synchronization Symbols (CSS), Global Synchronization Symbols (GSS) shared between two or more network edge nodes), common pilot symbols ( CPS), Paging Indicator Channel Symbol (PI), Answer Indicator Channel Symbol (AI), Other Indicator Channel (OI), Broadcast Indicator Channel (BI), Broadcast Control Channel Information (BCCH), and Paging Channel Information (PCH). These channels are commonly found in cellular communication systems and may have different names or not exist in some systems. Additionally, other control and synchronization channels may exist and transmit in this region.

Figure 15 shows an alternative radio frame structure of arbitrary size, where the synchronization and control (S+C) region is not part of the radio frame, but part of a larger hierarchical frame structure composed of radio frames, where each j radio frame transmission (S+C) regions. In this example, the radio frame after the S+C region is 18 subframes.

Figures 16 and 17 illustrate a hierarchical frame structure, where a superframe is defined, consisting of n+1 radio frames. In Fig. 16, both the radio frame and the superframe have a control region and a synchronization and control region, respectively, whereas in Fig. 17, only the superframe includes the control region. The radio frame control and synchronization regions may be of the same type or may be different for different radio frame positions in a superframe.

The synchronization and control portion of a radio frame may be all or part of one or more subframes and may be of fixed duration. It can also vary between radio frames depending on the hierarchy in which the sequence of radio frames is embedded. For example, as shown in Figure 16, it may include the first two subframes of each radio frame. In general, multiple subframes need not be directly adjacent to each other when there is synchronization and/or control in all or part of the multiple subframes. In another example, it may include two subframes in one radio frame and three subframes in another radio frame. Radio frames with extra subframe overhead do not occur frequently, and the extra overhead may occur in subframes adjacent or not adjacent to regular (frequent) radio frame overhead. In an alternative embodiment, the overhead may be located in the radio frame, but not an integer number of subframes, which may happen if the radio frame is not divided equally into subframes but into an overhead region plus an integer number of subframes. For example, a 10 ms radio frame may consist of 10 subframes, where each subframe has a length of 0.9 ms, plus a portion of 1 ms for radio frame overhead (eg, radio frame paging or broadcast channel).

As will be discussed below, the synchronization and control part of all or some radio frames may (but is not required) be configured to convey information about the layout of the radio frame, such as a mapping of short/long subframe configurations (example - if the radio frame has two long frames followed by a short frame, then the configuration can be denoted as L-L-S). Furthermore, the synchronization and control part may indicate which subframes are used for broadcasting, etc. Communicating the radio frame layout in this way would reduce or potentially eliminate the need to blindly detect the placement and usage of frames on a subframe-by-subframe basis, or to deliver the "scheduling" of radio frames via signaling at higher layers, or to define a limited number of frames in advance. (one of them is then selected and signaled to the user equipment at initial system access). It should be noted that regular data frames can also be used to carry Layer 3 (L3) messages.

framing control

There are several ways for subscriber stations (SS) 101-103 to determine the framing structure (and subframe type) in a radio frame. For example:

• Blind (eg, BS controls dynamically but not signaled, so SS has to determine frame start in radio frame. Frame start can be based on presence of pilot or control symbols in frame.)

Superframe (for example, BS transmits information specifying frame configuration every 1sec until the next superframe)

· System deployment (base station) and registration (mobile station)

· Signaled in the radio frame synchronization and control section

Signaled in the first frame of a radio frame (may declare mappings for other frames)

· In control assignments for allocating resources

In general, two or more frame durations and subframe types may exist in a radio frame. If the communication system 100 is configured such that the mix of short and long frames in a radio frame can vary, the possible start positions of long frames can be fixed to reduce signaling/searching. Signaling/searching can be further reduced if a radio frame has only a single frame duration or a single subframe type. In many cases, the determination of the framing structure of the radio frame also provides information about the location of control and pilot information in the radio frame, such as in the resource allocation control (next section) located in the second symbol of each frame at the starting point.

Certain control methods may be more suitable for traffic conditions that vary from frame to frame. For example, having a control map for each radio frame in a designated subframe (first in a radio frame, last in a previous radio frame) may allow efficient processing of large packets in one radio frame (e.g. , TCP/IP), and allows many VoIP users to be processed in another radio frame. Alternatively, if the user traffic type changes relatively slowly, superframe signaling is sufficient to change the control channel allocation in the radio frame.

Resource Allocation (RA) Control

A frame has an associated control structure (possibly the only one associated) that controls the usage (allocation) of the user's resources. Resource allocation (RA) control is typically provided for each frame and its respective frame duration in order to reduce delays when scheduling retransmissions. In many cases, the determination of the framing structure of the radio frame also provides information about the location of the resource allocation control (of each frame) in the radio frame, such as where the resource allocation control is located in each frame (long frame or short frame) ) at the start of the second symbol. The control channel is preferably TDM (e.g., one or more TDM symbols) and is located at or near the start of the frame, but may alternatively be spread over time (symbols), frequency (subcarriers), or both. in frame. One-dimensional or two-dimensional spreading and code division multiplexing (CDM) of control information can also be used, and depending on the system configuration, multiple multiplexing methods such as TDM, FDM, CDM can also be combined.

Typically, such as for TDM/FDM/CDM multiplexing, there are two or more user allocations in a frame, although limiting to a single user per frame is also possible, such as TDM. Therefore, when a control channel is present in a frame, it can allocate resources for one or more users. There may also be more than one control channel in a frame if separate control channels are used for the resource allocation of the two users in the frame.

The control field may also contain more information than the resource allocation for the frame. For example, on the downlink, the RA control may contain uplink resource allocation and acknowledgment information on the uplink. For fast scheduling and lowest latency, fast acknowledgments to individual frames may be preferred. Another example is that the control field can make persistent resource allocations that remain applicable for more than one frame (e.g. constant resource allocation for a specified number of frames or radio frames, or until passed by another frame in a different frame). control messages are turned off)

The control information in the first frame of a radio frame (or the last frame of a previous radio frame) may also provide framing for the next (or more generally, future) frame or the remainder of the radio frame (and thus providing a control position). Two additional changes:

• Overlapping control regions: Control channels of a first frame may be assigned to its own frame and some may be assigned to a second frame, and control channels in the second frame may additionally be assigned to the second frame. This capability may be useful for mixing different traffic types (eg VoIP and large packets) in a single radio frame.

additional scheduling flexibility in radio frames (partly ambiguous): the control channel in the first frame (or the framing control map in the radio frame) can give a slightly ambiguous statement about the control map of the radio frame, for more frame-by-frame flexibility. For example, a control map may indicate a frame/control location, either explicit or probable. The semi-blind receiver will know the unambiguous position and will have to blindly determine if a possible frame/control position is valid.

pilot symbol

Pilot or reference symbols can be multiplexed in a frame or in a subframe by TDM, FDM, CDM or various combinations thereof. Pilot symbols can be common (received and used by any user) or dedicated (for a specific user or a specific group of users), and there may be a mix of common and dedicated pilots in a frame. For example, a common pilot symbol (CPS) reference symbol may be the first symbol (TDM pilot) in a subframe, thereby providing substantially evenly spaced common pilot symbols throughout the radio frame. Downlink and uplink may have different pilot symbol formats. Pilot symbol allocation may be constant or may be signaled. For example, common pilot symbol positions may be signaled in the radio frame control of one or more RAFs. In another example, in the RA control of a frame, the dedicated pilots in the frame (in addition to any common pilots) are indicated.

In one embodiment, subframe definitions may be related to common pilot spacing. For example, if a subframe is defined to include a single common pilot symbol, the subframe length is preferably related to the minimum expected coherence time of the channel of the system being deployed. With this method, the subframe duration can be simply determined through the common pilot interval (of course, other ways of defining the subframe length are also allowed). Common pilot spacing is mainly determined by channel estimation performance, which is determined by coherence time, velocity distribution, and user modulation in the system. For example, there could be one pilot every 5 bauds to be able to handle 120 kph users in 50 μs baud (40 μs useful duration + 10 μs cyclic prefix or guard duration). It should be noted that the baud used here refers to the OFDM or DFT-SOFDM symbol period.

When the Doppler rate is very low, all or part of the common pilot can be omitted from a particular frame or subframe because, in this case, the control from the previous or subsequent subframe/frame, or from the radio frame Area pilots are sufficient for channel tracking. Also, if differential/non-coherent modulation is used, no pilot is required. However, for simplicity of illustration, each subframe is shown with pilot symbols.

uplink and downlink

The shown radio frame configuration can be used for uplink or downlink of an FDD system. An example for uplink and downlink is shown in FIG. 18 . Figure 18 shows uplink subframes, which have the same configuration as downlink subframes, but in general they may have a different number of symbols in each subframe, or even have different There are different numbers of subframes in a frame. The modulation used for the uplink can be different than for the downlink, eg DS-CDMA, IFDMA or DFT-SOFDM (DFT-Spread Spectrum-OFDM) instead of OFDM. The uplink radio frame is shown offset relative to the downlink radio frame structure to help with HARQ timing requirements by allowing faster acknowledgments, although a zero offset is also allowed. The offset can be any value, including a subframe, multiple subframes, or a fraction of a subframe (eg, a certain number of OFDM or DFT-SOFDM symbol periods). The first subframe in an uplink radio frame may be assigned as a common control/contention channel, such as a Random Access Channel (RACH) subframe, and may correspond to a downlink synchronization and control subframe. Control frames (or more generally, messages) carrying uplink control information, CQI, downlink Ack/Nack messages, pilot symbols, etc., may be time or frequency multiplexed with data frames.

Replaceable uplink

Two alternate FDD uplink structures are shown with only one frame duration on the uplink. However, two or more long frame types are defined. In FIG. 19 and FIG. 20 , a 2 ms long frame composed of 0.5 ms subframes has a frame type of long RACH, data (Data), or composite (Composite). Long RACH may occur infrequently, such as every 100ms. A composite frame has data, control and short RACH. The duration of the short RACH may be less than one subframe. A data frame (not shown) is similar to a composite frame, but replaces the short RACH with a data subframe. Control, RACH and pilot are all shown as TDM, but could also be FDM or a combination of TDM/FDM. As before, the subframe type is defined and it can be based on the guard interval duration, either for RACH frame or for IFDM/DFT-SOFDM&OFDM switching. Figure 21 is similar to Figures 19 and 20, but the frame has 6 subframes and type data or composite. If only composite data frames are used, each frame will contain control and short RACH. Long RACH occurs infrequently (shown once per subframe) for an integer (preferred) or non-integer number of subframes.

TDD

For Time Division Duplex (TDD), system bandwidth is allocated to uplink or downlink in a time multiplexed manner. In one embodiment, switching between uplink and downlink occurs every few frames, such as every radio frame. Uplink and downlink subframes can be the same or different duration, with the "TDD split" determined by the subframe granularity. In another embodiment, the downlink and uplink occur in long frames having two or more subframes, with a possibly fixed duration. Short frames with a single subframe are also feasible, but backhauling within a frame is difficult or costly in terms of overhead. The uplink and downlink can be of the same or different duration, and the "TDD partition" is determined by subframe granularity. In either of the two embodiments, TDD overhead such as ramp-up and ramp-down may be included inside or outside the subframe.

Scalable Bandwidth

Transmissions can occur on one of two or more bandwidths, where the radio frame duration is the same for each bandwidth. The bandwidth can be 1.25, 2.5, 5, 10, 15 or 20 MHz or some approximation. The subframe duration (and thus the smallest possible frame duration) is preferably the same for each bandwidth, as is the set of available frame durations. Alternatively, a subframe duration and multiple frame durations may be configured for each bandwidth.

Table 4 shows an example of 6 carrier bandwidths with a subcarrier spacing of 22.5 kHz, and Table 5 shows an example of 6 carrier bandwidths with a subcarrier spacing of 25 kHz. It should be noted that in Table 5, the guard interval (eg, cyclic prefix length) of each symbol in a subframe is not constant, as described in the "Subframe Types" section. In a subframe, all symbols may have different symbol durations due to different guard durations (cyclic prefixes). For this example, all excess samples are given for a single symbol; in other examples, two or three additional guard interval values may be defined for a subframe. As another example, for a subcarrier spacing of 15 kHz and a subframe duration of 0.5 ms, a short frame of 7 symbols may have an average CP of ~4.7 μs (microseconds), and a short frame of 6 symbols may have an average CP of ~4.69 μs ( 9 samples at 1.25 MHz, scaled for higher bandwidth) and an average CP of ~5.21 μs (10 samples at 1.25 MHz, scaled for higher bandwidth).

parameters Carrier Bandwidth (MHz) 20 15 10 5 2.5 1.25 Frame duration (ms) 0.5 0.5 0.5 0.5 0.5 0.5 FFT size 1024 768 512 256 128 64 Subcarrier (occupied) 768 576 384 192 96 48 Symbol duration (μs) 50 50 50 50 50 50 Useful (μs) 44.44 44.44 44.44 44.44 44.44 44.44 Protection (μs) 5.56 5.56 5.56 5.56 5.56 5.56 protection (sample) 128 96 64 32 16 8 Subcarrier Spacing (kHz) 22.5 22.5 22.5 22.5 22.5 22.5 Occupied BW(MHz) 17.28 12.96 8.64 4.32 2.16 1.08 symbol for each frame 10 10 10 10 10 10 16QAM data rate (Mbps) 49.15 36.86 24.58 12.29 6.14 3.07

Table 4 - OFDM numerical nomenclature scheme for different carrier bandwidths of regular (data) subframes

parameters Carrier Bandwidth (MHz) 20 15 10 5 2.5 1.25 Frame duration (ms) 0.5 0.5 0.5 0.5 0.5 0.5 FFT size 1024 768 512 256 128 64 Subcarriers (occupied) 736 552 368 184 96 48 Symbol duration (μs) 45.45 45.45 45.45 45.45 45.45 45.45 Useful (μs) 40.00 40.00 40.00 40.00 40.00 40.00 Protection (μs) 5.45 5.45 5.45 5.45 5.45 5.45 protection (sample) 139.64 104.73 69.82 34.91 17.45 8.73 Rule protection (μs) 5.43 5.42 5.39 5.31 5.31 5.00 Irregular protection (μs) 5.70 5.83 6.09 6.87 6.87 10.00 Subcarrier Spacing (kHz) 25 25 25 25 25 25 Occupied BW(MHz) 18.4 13.8 9.2 4.6 2.4 1.2 subchannel 92 69 46 twenty three 12 6 symbol for each frame 11 11 11 11 11 11 16QAM data rate (Mbps) 52.99 39.74 26.50 13.25 6.91 3.46

Table 5 - OFDM numerical nomenclature scheme for different carrier bandwidths of regular (data) subframes

ARQ

ARQ and HARQ can be used to provide data reliability. The (H)ARQ process may be different or shared across multiple subframe types (eg, regular and broadcast), and across multiple frame durations. In particular, retransmissions with different frame durations can be enabled or disabled. For fast scheduling and lowest latency, fast acknowledgments corresponding to individual frames may be preferred.

HARQ

For ARQ, the multi-frame concept can be used for reliability, or for HARQ, for extra reliability. The ARQ or HARQ scheme may be a stop and wait (SAW) protocol, a selective retransmission protocol, or other schemes known in the art. The preferred embodiment described below will use multi-channel stop-and-wait HARQ modified for multi-frame operation.

The number of channels in N-channel SAW HARQ is set based on the round-trip transmission (DTT) delay. Enough channels are defined such that the channels can be continuously fully occupied by data from one user. Therefore, the minimum number of channels is 2.

If the round trip time is proportional to the frame length, both short and long frames can use the same N (eg, 3) channels. If the round trip time is relatively constant, then the number of channels required for short frame durations will be greater or the same as the number of channels required for long frame durations. For example, for subframes and short frames of 0.5 ms, and long frames of 3 ms, and also assuming a backhaul time of 1 ms between transmissions (i.e. effective receiver processing time to decode the transmission and then pass the required feedback ( response such as Ack/Nack), then 3 channels are used for short frames and 2 channels are used for long frames.

If there is infrequent switching from one frame size to another, and there is no mixing of frame durations in radio frames, the existing procedure can be terminated by frame size switching, and the number of channels per frame size and HARQ signaling can be independent. In the case of a dynamic frame duration or TTI, the number of concatenated subframes may vary dynamically, at least for initial transmissions and possibly for retransmissions. If retransmission of packets is allowed to occur on different frame types, the HARQ process can be shared between frame durations (eg, the HARQ process identifier can refer to a short frame or a long frame either explicitly or implicitly). The required number of channels can be defined based on the multiplexing of a sequence of all short frames or all long frames, taking into account whether packets have a relatively fixed or proportional backhaul (eg, decoding and ACK/NACK transmission). For a fixed backhaul, N can be determined mainly based on short frame multiplexing requirements. For proportional backhaul, the N required for short frame and long frame multiplexing can be about the same. Designing N to handle arbitrary switching between short and long frames may require additional HARQ channels (larger N). For example, considering the requirement of N=3 multiplexed for each short frame or long frame (proportional backhaul), a long frame is equal to four short frames in duration. Obviously, the sequences used by the HARQ channel can be all short (1, 2, 3, 1, 2, 3...) or all long (1, 2, 3, 1, 2, 3...), There are no restrictions. However, a long frame (with channel ID 1) must be followed by an equivalent span of two long frames before channel 1 can be used to retransmit either a short frame or a long frame. In the span of these two long frames, channels 2 and 3 are available for short frames, but at this point, since channel 2 cannot yet be reused and channel 1 is not available, an additional channel 4 must be used. For N<=(number of short frames in a long frame), the total number of channels required may be N+(N-1). Continuing with the example above, one can see that if two long frames (channel IDs 1 and 2) are followed by a short frame, channel IDs 3 and 4 and 5 are required before channel 3 can be reused. In this example, five channels are more than the three channels required for either of the two to be multiplexed independently.

Multidimensional (time, frequency and space) HARQ

It is more efficient (eg, in terms of coding and resource allocation granularity) to allow remote units 101-103 to be scheduled with more than one packet for a given frame or scheduling entity than defining N based solely on roundtrip time. Instead of assuming one HARQ channel per frame for the remote unit, up to N2 HARQ channels are considered. Thus, assuming N-channel stop-and-wait HARQ, where N is purely based on backhaul time, and there will also be N2 HARQ channels per frame for the remote unit, each remote unit supports up to NxN2 HARQ channels. For example, each consecutive long frame will correspond to an N-channel stop and wait for one of the N channels of the HARQ protocol. Since each long frame consists of "n" subframes, if each subframe is also allowed to be a HARQ channel, we will have up to Nxn HARQ channels per remote unit. Therefore, in this case, the independently answerable unit would be a subframe, not a long frame. Alternatively, if "p" frequency bands are defined per carrier, each can be a HARQ channel, resulting in up to Nxp HARQ channels per mobile unit. More generally, for "s" spatial channels, there may be up to "n" x "p" x "s" x "N" HARQ channels per mobile unit. The parameter "n" would be even larger if it is defined based on OFDM symbols and there are "j" OFDM symbols per subframe. In any case, as with unmodified HARQ, the channel cannot be re-used until the time limit associated with N has elapsed.

Another way to measure the number of HARQ channels is to determine the maximum number of packets of maximum length that can be allocated on a frame, such as a maximum modulation and coding rate and packets of 1500 bytes (+overhead). Smaller packets can be concatenated to the largest aggregate packet size for the channel. For example, if N=2 (for minimum round trip time (RTT)), and if 4 packets are transmitted in subframes with 64QAMR=3/4 and closed-loop beamforming implemented, then 8=2×4 channels are required for A short frame, and a long frame requiring 32 channels for 4 subframes. The number of channels can be further adjusted in this example if retransmissions of packets are allowed to occur on different frame types, as above.

Control signaling will need to be modified to support HARQ signaling modified for short/long frames or for HARQ channels that are not fully metered based on backhaul time. In one embodiment corresponding to EUTRA application, for the currently used "New Data Indicator (NDI)", "Redundancy Version Indicator (RVI)", "HARQ Channel Indicator (HCI)", and "Transport Block size (TBS)" and ACK/NACK and CQI feedback. Other technical specifications may use similar naming schemes for HARQ. In one example, up to "n" or "p" remote unit packets may be sent in one long frame transmission. Each packet may be assigned separate frequency selective (FS) or frequency diverse (FD) resource elements and mutually distinct control signaling attributes (NDI, RVI, HCI and TBS). Color coding, such as utilizing the identity of the remote unit to assist in cyclic redundancy check (CRC) calculations, can be applied to the CRC of each downlink packet to indicate the target remote unit. Some extension of the HCI field (eg, number of bits = log ₂ ('n'x'N')) will be required to correctly perform soft buffer combining for packet transmission. Similarly, ACK/NACK feedback will likely require an HCI field or color coding to indicate which set of packets of the remote unit in a short or long frame transmission is being ACK or NACK.

frequency selective allocation

Figure 22 and Figure 23 show short frame frequency selective (FS) and frequency diversity (FD) resource allocation for several users, respectively. For FS scheduling, a resource element (or resource block or resource unit or chunk) is defined to consist of multiple subcarriers, whereby the carrier bandwidth is divided into a number (preferably an integer number) of assignable REs (e.g., with A 5 MHz carrier of 192 subcarriers each has 24 REs of 8 subcarriers). To reduce signaling overhead and better match the channel-dependent bandwidth of typical channels (e.g., 1 MHz for pedestrian B, and 2.5 MHz for vehicle A), REs can be defined as px8 subcarriers, where "p" can be 3, and still provide the resolution needed to achieve most of the FS scheduling benefits. The number of subcarriers used as a basis for multiple subcarriers can also be set to a number other than 8 (e.g. such that if the number of subcarriers is 300 at 5 MHz, the total RE size is 15 or 25, or if the subcarriers The number of carriers is 288, which means 24 subcarriers).

In FIG. 24, similarly, FS and FD resources can be allocated in the same long frame. However, it is preferred that FS and FD resources are not allocated on the same time interval to avoid resource allocation conflicts and signaling complexity.

Although the present invention has been particularly shown and described with reference to particular embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention. . It is intended that such changes come within the scope of the claims. For example, in the case of a transmission system comprising multiple discrete carrier frequencies, signaling or pilot information in a frame may occur on some component carrier frequencies but not others. Furthermore, pilots and/or control symbols may be mapped to time-frequency resources after a process of "bandwidth spreading" via direct sequence spreading or code division multiplexing methods. In another example, the frame structure can be used with MIMO, smart antennas, and SDMA, with the same or different frame durations for simultaneous SDMA users.

Claims (11)

1. A method for reducing round-trip delay in a communication system, said method comprising the steps of: receiving data to be transmitted on a radio frame, wherein the radio frame consists of a plurality of subframes; selecting a frame duration from two or more feasible frame durations, where a frame is substantially equal to a number of subframes; arranging the data in the plurality of subframes to produce a plurality of data subframes; and The frame having the plurality of data subframes is transmitted on the radio frame. 2. The method of claim 1, wherein the frame is divided into a plurality of equally sized subframes. 3. The method of claim 1, wherein the radio frame is a 10 millisecond radio frame. 4. The method of claim 1, wherein the radio frame comprises a short frame and a long frame, wherein each short frame comprises a first plurality of subframes and each long frame comprises a second plurality of subframes. 5. The method of claim 4, wherein the radio frame further includes a control signaling portion. 6. A method for communicating data in a communication system, said method comprising the steps of: receiving data to be transmitted on a radio frame, wherein the radio frame includes a plurality of subframes; selecting a frame, wherein the frame is substantially equal to a plurality of subframes; arranging the data in the plurality of subframes to produce a plurality of data subframes; positioning a common pilot in each subframe of the plurality of subframes; and The frame having the plurality of data subframes is transmitted on the radio frame. 7. The method of claim 6, wherein the common pilots comprise reference symbols. 8. The method of claim 6, wherein at least a portion of the common pilot is time division multiplexed on the first symbol of the frame. 9. The method of claim 6, wherein the common pilot is further positioned in the plurality of subframes in the radio frame. 10. The method of claim 6, wherein the common pilots are substantially evenly spaced in the radio frame. 11. The method of claim 6, wherein every three or four OFDM symbols are substantially evenly spaced in the radio frame.

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