HK1117299A - Timing synchronization and channel estimation at a transition between local and wide area waveforms using a designated tdm pilot - Google Patents

Description

Timing synchronization and channel estimation using assigned TDM pilots when transitioning between local and wide-area waveforms

35 priority claims according to U.S.C. § 119

The present application claims the benefit of U.S. provisional patent application serial No. 60/660,720, entitled "timing SYNCHRONIZATION detection methods INA WIRELESS COMMUNICATION SYNCHRONIZATION NETWORK" filed ON 10/3/2005, which is hereby incorporated by reference in its entirety.

Technical Field

The subject technology relates generally to communication systems and methods, and more particularly, to systems and methods that perform enhanced time synchronization and channel estimation for wireless networks.

Background

Orthogonal Frequency Division Multiplexing (OFDM) is a method of digital modulation in which a signal is divided into several narrowband channels at different frequencies. These channels are sometimes referred to as subbands or subcarriers. This technique was originally conceived during research to minimize interference between channels that are close to each other in frequency. In certain aspects, OFDM is similar to conventional Frequency Division Multiplexing (FDM). The difference is in the way the signal is modulated and demodulated. Generally, priority is given to minimizing interference or cross-talk among channels and symbols comprising the data stream. Perfecting individual channels is not particularly important.

In one area, OFDM has been used for european digital audio broadcasting services. This technology is applicable to digital televisions and is being considered as a method of obtaining high-speed digital data transmission through a conventional telephone line. It is also used in wireless local area networks. Orthogonal frequency division multiplexing may be considered to be an FDM modulation technique for transmitting large amounts of digital data over radio waves, where OFDM operates by splitting a radio signal into multiple smaller sub-signals or sub-carriers, which are then transmitted simultaneously to the receiver at different frequencies. One advantage of OFDM technology is that it reduces the amount of crosstalk interference in signal transmissions, where current specifications, such as 802.11a WLAN, 802.16 and WiMAX technologies, employ various OEDM aspects.

In some systems that deploy OFDM technology, transmissions are intended for many users simultaneously. One example of this is a broadcast or multicast system. Furthermore, the data in each transmission is typically Time Division Multiplexed (TDM) if different users can choose between different parts of the same transmission. It is often the case that data intended for transmission is organized into a fixed structure, such as a frame or superframe. Different users may thus choose to receive different portions of a superframe at any particular time. To help most users synchronize the timing and frequency of the broadcast signal, Time Division Multiplexed (TDM) pilot symbols are sometimes inserted at the beginning of each superframe. In one such scenario, each superframe begins with a header consisting of two TDM pilots (referred to as TDM pilot 1 and TDM pilot 2) and other parts. These symbols are used by the system to achieve initial frame synchronization, also referred to as initial acquisition.

To further aid in time and/or frequency synchronization, also referred to as time or frequency tracking, in one superframe, additional pilot symbols may be used. Time and frequency tracking may be achieved using Frequency Division Multiplexed (FDM) pilots, which may be embedded in each transmitted data OFDM symbol. For example, if each OFDM symbol consists of N subcarriers, N-P of them may be used for data transmission, and P of them may be allocated to the FDM pilot. These P FDM pilots are sometimes evenly distributed over N subcarriers so that every second pilot is decomposed by N/P-1 data subcarriers. A uniform subset of such subcarriers within one OFDM symbol is called interleaving.

The time domain channel estimate is used for time tracking during a superframe. The time domain channel estimate is obtained from FDM pilots embedded in the data OFDM symbols. The FDM pilots may be placed on the same interlace all the time, or they may occupy different interlaces in different OFDM symbols. The subset of subcarriers with index i +8k is sometimes referred to as the ith interlace. In this case, N/P is 8. In one case, the FDM pilot may be placed on interlace 2 during one OEDM symbol, on interlace 6 during the next symbol, then on interlace 2, and so on. This is called the (2, 6) interval pattern. In other examples, the pilot spacing pattern may be more complex such that the occupied interlaces are described as a (0, 3, 6, 1, 4, 7, 2, 5) pattern. This is sometimes referred to as a (0, 3, 6) spacing pattern. The different spacing patterns enable the receiver to obtain channel estimates longer than the P time-domain taps. For example, a (2, 6) spacing pattern may be used at the receiver to obtain a length 2P channel estimate, while a (0, 3, 6) spacing pattern may result in a length 3P channel estimate. This is achieved by combining the channel observations of length P from successive OFDM symbols into a longer channel estimate in a unit called a time filtering unit. Longer channel estimates may generally result in a more robust timing synchronization algorithm.

Some broadcast systems are intended for different types of transmission simultaneously. For example, some broadcast data may be used for any potential user within a wide area network, and such data is referred to as wide area content. Other data symbols transmitted over the network may be used only for users currently residing in a particular, local portion of the network. Such data is called local area content. The data OFDM symbols belonging to different contents may be time-division multiplexed within each frame in one superframe. For example, some portions of each frame within a superframe may be reserved for wide-area content, while other portions are used for local content. In this case, data and pilots used for different contents may be scrambled using different methods. Furthermore, the set of transmitters that broadcast the wide-area and local content simultaneously within a superframe may be different. Thus, time domain channel estimates and channel observations related to wide-area content are quite common, and time domain channel estimates and channel observations related to local content can be quite different.

In the above-described case, channel estimation for OFDM symbols aggregated in the vicinity of the boundary between the wide-area and local waveforms requires a special strategy to be employed. This is because the channel observations from the wide-area symbols cannot be combined in a seamless manner with the channel observations from the local symbols. A similar concept applies to time tracking of OFDM symbols located shortly after the waveform boundary. If time tracking is based on time domain channel estimation and if a single channel estimation requires views from three sequential OFDM symbols, time tracking cannot be performed during the first few OFDM symbols after the waveform boundary. Therefore, alternative channel estimation and timing synchronization techniques may be needed.

Disclosure of Invention

The following presents a simplified summary of various embodiments in order to provide a basic understanding of some aspects of the embodiments. This summary is not an extensive overview. It is not intended to identify key/critical elements or to delineate the scope of the embodiments disclosed herein. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.

Receiver processing components and methods are provided for wireless networks. In addition to TDM pilots 1 and 2, at least one additional Time Domain Multiplexed (TDM) pilot symbol, which may be referred to as TDM3 or TDM pilot 3 in one example, is processed at the wireless receiver along with other superframe symbols and parameters on which aspects such as time synchronization and channel estimation are performed. In one embodiment, a receiver component is provided that can take into account previously unaccounted for issues with timing and channel estimation due in part to the fact that: the pilot symbols and associated data are not scrambled in a similar manner from one waveform boundary to another (e.g., local to wide area boundary). Given the nature and structure of the added pilot symbols, this can be performed on either side of the local and wide-area waveform boundaries that occur in one data frame.

In another embodiment and as described above, at least one additional TDM pilot symbol is added to a regular set of broadcast symbols (e.g., a set including TDM1 and TDM2) at regular or deterministic intervals within a superframe broadcast. In this case, TDM3, TDM4, etc. pilot symbols may be added to an existing set of pilots to alleviate timing and channel estimation problems within an Orthogonal Frequency Division Multiplexing (OFDM) network for multimedia data transmission organized in superframes, where different portions of the superframe are used for different waveform transmissions. For example, a number of TDM3 symbols may be processed at various boundaries from a set of symbols and placed at waveform boundaries in the superframe to facilitate synchronization and channel estimation. Similar to TDM pilot 2, TDM pilot 3 (or a subset of symbols) may be designed to provide timing synchronization and channel estimation, except that TDM pilot 2 is limited to wide-area channels and TDM pilot 3 may be used for both wide-area and local channels depending on the location in the superframe. The structure of TDM pilot 3 may be different from the structure of TDM pilot 2. If TDM pilot 3 (or other additional pilot) is located between transitions from wide-area waveform to local waveform in the super-frame, it can be used for wide-area channel estimation or local channel estimation and timing. The TDM pilot 3, if placed on the transition from local to wide area, can be used for local channel estimation or wide area timing and channel estimation.

To the accomplishment of the foregoing and related ends, certain illustrative embodiments are described herein in connection with the following description and the annexed drawings. These aspects are indicative of, and cover all, the various ways in which the embodiments may be practiced.

Drawings

Fig. 1 is a simplified block diagram illustrating a wireless communication network employing an enhanced superframe structure and receiver processing components.

Fig. 2 shows an example superframe structure with additional pilot symbols.

Fig. 3 shows an example pattern of one additional pilot symbol.

Fig. 4 illustrates an alternative embodiment in which multiple TDM pilot-3 symbols are used between local and wide-area boundaries.

Fig. 5 shows an example pattern for additional timing pilot symbols.

Fig. 6 shows an example structure of a TDM pilot 3 symbol for reception.

Fig. 7 shows the concept of channel segments (bins) and an example of channel estimation for timing synchronization.

Fig. 8 illustrates an example block diagram of a timing synchronization algorithm with respect to local/wide area data boundaries.

Fig. 9 illustrates an example pilot symbol processing for a wireless system.

Fig. 10 is a diagram illustrating an example user equipment for a wireless system.

Fig. 11 is a schematic diagram illustrating an example base station for a wireless system.

Fig. 12 is a schematic diagram illustrating an example transceiver for a wireless system.

Detailed Description

Systems and methods for channel estimation and timing synchronization in a wireless network are provided. In one embodiment, a method for time synchronization at a radio receiver is provided. The method includes decoding at least one new TDM pilot symbol in addition to TDM1 and TDM2 and processing the new TDM pilot symbol from a channel boundary of an OFDM broadcast to perform time synchronization for a wireless receiver. A method for channel estimation at a wireless receiver is also provided. This includes decoding at least one new TDM pilot symbol and receiving the new TDM pilot symbol from the OFDM broadcast to facilitate channel estimation for the wireless receiver.

In another embodiment, a method for channel estimation, time synchronization, and AGC bootstrapping for data symbols located near boundaries between different types of traffic in a multicast wireless system using Time Division Multiplexed (TDM) pilot symbols is provided. The method includes determining at least one new TDM pilot symbol in addition to the TDM1 symbol and the TDM2 symbol. The method also includes inserting at least one new TDM pilot symbol between two OFDM symbols belonging to different broadcast waveforms to facilitate decoding the OFDM transport block before or immediately after the boundary. The new TDM pilot symbols may be used for channel estimation, time synchronization, and for Automatic Gain Control (AGC) bootstrapping, or other aspects.

As used in this application, various wireless communication terms are employed. For wireless transmission, the packet structure on transmission may comprise an Orthogonal Frequency Division Multiplexing (OFDM) symbol consisting of 4642 time-domain baseband sample values called OFDM chips. Among these OFDM chips are 4096 data and pilot chips derived from 4096 data and pilot subcarriers in the frequency domain. These chips are periodically spread with 529 chips before the useful portion and 17 chips after the useful portion. To reduce the out-of-band energy of the OFDM signal, the first 17 chips and the last 17 chips in one OFDM symbol have a raised cosine envelope. The first 17 chips of one OFDM symbol overlap with the last 17 chips of the OFDM symbols preceding them. Thus, the duration of each OFDM symbol is 4625 chips long.

In one example of transmitting data packets, the data may be generally organized into superframes, with each superframe having a second duration. One superframe consists of 1200 symbols OFDM-modulated with 4096 subcarriers. Relative to subcarriers, staggering refers to a subset of subcarriers spaced by some amount (8's spacing). For example, 4096 subcarriers may be divided into 8 interlaces, where the subcarriers in the ith interlace are the subcarriers with index 8k + i. Among 1200 OFDM symbols of one superframe, there are: two TDM pilot symbols (TDM1, TDM 2); a wide area and a local identification channel (WIC and LIC) symbol; fourteen Overhead Information Symbol (OIS) channel symbols; a variable number of 2, 6, 10, or 14 pilot position symbol (PPC) symbols to aid in positioning; a certain number of pilot channel (TPC) symbols, or TDM3 pilots, located at respective boundaries between wide area and local content data; the remaining symbols are used for the broadcast of a wide or local area waveform. Each super-frame consists of four data frames and overhead symbols.

Time Division Multiplexed (TDM) pilot symbol 1(TDM1) is the first OFDM symbol of each superframe, where TDM1 is periodic and has 128 OFDM chip periods. The receiver uses TDM1 for frame synchronization and initial time (run time) and frequency acquisition. Following TDM1 are two symbols, which carry wide area and local IDs, respectively. The receiver uses this information to perform the appropriate descrambling operations for the corresponding content using the corresponding PN sequence. Time division multiplexed pilot symbol 2(TDM2) follows the wide and local ID symbols and contains two and a fraction of a period, where TDM2 is periodic with 2048 OFDM chip periods. The receiver uses TDM2 when determining the exact timing for demodulating the OIS channel.

Following TDM2 is: a wide area tpc (wtpc) symbol; five wide-area OIS symbols; five wide area FDM pilot symbols; another WTPC; a local tpc (ltpc) symbol; five local OIS symbols; five local FDM pilot symbols; another LTPC; and four data frames following the first 18 OFDM symbols as described above. The data frame is subdivided into a wide data portion and a local data portion. The wide-area waveform is pre-determined and a wide-area TPC is appended to each end. This configuration is also used for the partial data portion. In this embodiment, there are a total of 10 WTPCs and 10 LTPC symbols per superframe.

In another embodiment, each transition between wide and local waveforms is associated with a single TPC pilot symbol. The structure of the unique TPC pilot is different from that of either the WTPC or LTPC symbols because the single pilot symbol is designed to meet both wide-area and local-area channel estimation and synchronization requirements. In this embodiment, there are a total of 11 TPC pilots (or TDM pilot 3 symbols) per superframe.

As used in this application, the terms "component," "network," "system," "module," and the like are intended to refer to a computer-related entity, either hardware, a combination of hardware and software, or software in execution. For example, a component may be, but is not limited to being, a process running on a processor, an object, an executable, a thread of execution, a program, and/or a computer. By way of example, both an application running on a communication device and the device can be a single component. One or more components can reside within a process and/or thread of execution and a component may be localized on one computer and/or distributed between two or more computers. In addition, these components can execute from various computer readable media having various data structures stored thereon. The components may communicate over local and/or remote processes such as in accordance with a signal having one or more data packets (e.g., data from one component interacting with another component in a local system, distributed system, and/or across a wired or wireless network such as the internet).

Fig. 1 shows a wireless network system 100. The system 100 includes one or more transmitters 110 that communicate over a wireless network with one or more receivers 120. The receiver 120 may comprise substantially any type of communication device, such as a cellular telephone, a computer, a personal assistant, a handheld or laptop device, and so forth. The system 100 employs a plurality of enhanced superframe components 130 to facilitate various determinations in the system 100. It should be noted that although the transmitters 110 may be employing the same superframe structure 130, different application data may be transmitted from the respective transmitters within the respective structures associated with each transmitter. In one embodiment, at least one additional Time Domain Multiplexed (TDM) pilot symbol is added to the set of broadcast symbols at regular or deterministic intervals within the superframe broadcast depicted at 130. Thus, TDM3, TDM4 (or more) pilot symbols may be added to an existing pilot set at 130 to mitigate time and channel estimation problems at the boundary between wide-area and local data waveforms within an Orthogonal Frequency Division Multiplexing (OFDM) network.

As will be described in greater detail below, the additional symbols are processed at the receiver 120 as a subset of symbols, where the subset may include one or more additional TDM3 symbols that facilitate symbol decoding of data symbols located near the boundary between the local and wide-area data waveforms. In one example, two subsets of symbols for TDM3 may be received and processed at receiver 120, where the subsets occur between local and wide-area boundary locations in superframe component 130. Thus, various embodiments may be provided. In one embodiment, a TDM pilot-3 symbol may be processed at each boundary of the superframe 130, and the structure and processing of such a pilot at the receiver 120 may be more complex. In other embodiments, two (or more) TDM pilot 3 symbols (with simpler structure and processing at the receiver) may be employed at most of the boundaries, except just after TDM pilot 2, and just before PPC symbols (which is described in more detail with respect to fig. 2).

One or more receiver processing components 140 are provided to decode the superframe 140 and employ the added TDM pilot symbols for aspects such as timing synchronization and channel estimation, where such components 140 are generally shown and adapted for a particular receiver 120. For example, TDM pilot 3 based timing synchronization may be based in part on principles similar to synchronization based on TDM pilot 2 used during initial acquisition. Furthermore, the algorithm for TPC pilot symbol based timing synchronization will depend on whether single or dual symbol TPC is employed on the waveform boundaries. However, the means 140 for the embodiment is typically more complex, especially if there is a single TPC pilot, since the pattern of pilot interlaces used in the single TPC symbol case is typically not fixed from one boundary to another. Thus, the respective mode can be determined to be related to the symbol index, and based on this information and assumptions about the channel position, the component 140 at the receiver 120 can select an appropriate set of combining coefficients. Based on the analysis, it may be desirable to perform at least the time tracking algorithm employed on the data symbols within the wide area and local traffic blocks depending on the timing synchronization of the TDM pilot 3 placed on the waveform boundaries. In addition to timing synchronization, the structure of the TDM pilot 3 (or other added pilot symbol) allows channel estimation for this symbol, which relies on both sides of the boundary between the wide area and local data waveforms.

Additionally, the system 100 can include a pilot symbol protocol for a wireless receiver. This may include means for decoding at least one additional pilot symbol for the super frame that is additional to TDM1 and TDM2 (e.g., the demodulator of reference numeral 120, described below). Further, the protocol includes means for receiving the superframe in the wireless network (e.g., marker 120), and means for processing the superframe to perform at least one of channel estimation and timing synchronization (e.g., marker 140).

Fig. 2 shows an example superframe structure 200. Although only one additional pilot symbol TDM3 is shown in the exemplary superframe 200, it should be understood that more than one additional pilot symbol may be employed. The superframe structure 200 introduces new OFDM symbols to facilitate the broadcast of multiple wide area channels and multiple local channels in a wireless network. The first OFDM symbol of the superframe is typically TDM pilot 1 at 210, with TDM pilot 2 of the second OFDM symbol shown at 220. This sequence is followed by a first TDM pilot 3 at 230, followed by a wide-area OIS (overhead information symbol) at 240. Typically, a new local TDM pilot 3 symbol 230 may be inserted before the local OIS symbol. This pattern is typically repeated at all nodes between the wide area and local channels, such as at reference 250. It should be noted, however, that simpler processing may occur if a subset of symbols having at least two symbols is disposed on the boundary between the wide area and the local area, such as 250. Similar to TDM pilot 2220, TDM pilot 3230, etc. can have four null-odd interlaces (1, 3, 5, 7), with even interlaces (0, 2, 4, 6) occupied by pilots. Unlike TDM pilot 2220, TDM pilot 3230 may employ three of the four even interlaces for the local pilot and one for the wide area if set in the transition from wide area to local area, or three for the wide area pilot and one for the local if TDM pilot 3 is set in the transition from local to wide area. This also applies to embodiments that employ a single TPC pilot on each boundary. In another embodiment, two TPC symbols are set by means of respective boundaries, a Locally Transitional Pilot Channel (LTPC) symbol having interlaces each occupied by a local FDM pilot, and a wide area TPC (wtpc) symbol having interlaces each occupied by a wide area FDM pilot. As can be appreciated, other configurations for the superframe 200 are possible.

As a reference, 290 data symbols per frame 200 may be employed. Two new OFDM symbols, one wide area 260 and local identification 270 channel (WIC and LIC) are introduced between TDM1 and TDM2 at the beginning of the superframe 200. In the remainder of the superframe 200, for example, 20 TDM3 pilot symbols 250 are introduced. In another embodiment, 11 TDM3 pilot symbols are introduced. Typically, in embodiments with two TDM3 pilots, there are two dedicated OFDM symbols at each transition between the wide and local channels. However, exceptions may exist. Before the PPC symbol, as represented by the shorter segments of TDM3 indicated by 230 and 280 for fig. 2, there is only one TDM3 symbol before the first wide-area OIS symbol (WOIS), and one at the end of the last frame.

A new Positioning Pilot Channel (PPC) may be added at 290 and includes P OFDM symbols at the end of the super frame. The positioning pilot helps to find the location of the receiver via triangulation methods.

Table 1: position of TDM pilot 3 in embodiments with two TPC symbols per boundary, W: number of wide-area symbols per frame, P: number of positioning pilots

Conversion	Symbol index for wide area TDM3 symbols	Symbol index for partial TDM3 symbols
			TDM2→W-OIS	4	-
W-OIS→L-OIS	10	11
			L-OIS→W-Data	18	17
W-Data→L-Data	19+W+(F+4)*i，(i＝0，1，2，3)	20+W+(F+4)*i，(i＝0，1，2，3)
			L-Data→W-Data	18+(F+4)*i，(i＝1，2，3)	17+(F+4)*i，(i＝1，2，3)
L-Data→Pos.pilots	--	1199-P

The locations of the TDM3 symbols are shown above in table 1, with this embodiment having both wide area TDM pilot 3 symbols and local TDM pilot 3 symbols. The number of useful data OFDM symbols per frame is denoted by F, W for the wide area channel and (F-W) for the local channel, where W ranges from 0 to F. As mentioned previously, the reference value of F may be 290, which corresponds to the reference value of six positioning pilots (P ═ 6). However, if no positioning pilot is used, at least 2 symbols should be reserved by means of current numerical constraints. When P is 2, the number of symbols per frame may increase from 290 to 291. One relationship between F and P is given by:

it should be noted that from the above description of TDM pilot 3 symbol positions, the TDM pilot 3 symbol may also be interpreted as being part of a frame. In particular, the frame 200 may begin with a wide-area TDM3 symbol at the beginning and end with a local TDM3 symbol at the end, and may include two TDM3 symbols at the transition from wide-area to local-area within the frame. By virtue thereof, the number of symbols per frame will be F +4, which is also a factor in table 1 above. Similarly, TDM3 symbols around the OIS may be included in the OIS, resulting in 7 wide-area OIS and 7 local OIS symbols, with individual OIS phases starting and ending in a TDM3 symbol. Whether TDM3 symbols are considered part of the frame and OIS is a matter of convention, but may also be driven to provide convenience for the hardware. In embodiments with a single TPC symbol, this simple analogy is not allowable, since there are typically F +2 symbols per frame, except for one frame (first or last) that contains F +3 symbols.

Fig. 3 illustrates an example interleaving pattern 300 for a single TPC symbol occurring at a waveform boundary. As described above, one symbol, referred to as TDM pilot 3, is used on each local/wide-area and wide/local boundary. The structure of this symbol is shown in fig. 3. Interlaces 0, 2, and 6 (in this example) are occupied by wide-area pilots at 310, 312, and 314, respectively. Interlace 4 is used for local pilots at 320. The abbreviation "ctpn" corresponds to channel estimation and timing wide-area pilot. In other words, this interlace can be used by the channel estimation block in a wide-area manner as a "previous symbol" FDM pilot interlace for demodulating the first wide-area symbol, and also for timing synchronization. Similarly, "cp 1" represents the pilot interlace used for the local channel estimation block when obtaining the "future symbol" channel observation. This observation is used to demodulate the last partial traffic symbol. Pilot interlaces denoted by "tp" are used for timing synchronization of data symbols in the following region. These interlaces 310-320 are separated by empty interlaces with no energy transfer. To maintain the total transmit energy constant among all OFDM symbols (including symbols with all occupied interlaces), the non-zero interlaces in the TPC pilot are being scaled up by a factor of *. When using pilots represented by "cp 1" and "cpn" (which implies, among other things, that the receiver knows the boundaries), the local and wide-area channel estimation blocks should take these issues into account.

The channel estimation pilot follows the occupation pattern of the adjacent corresponding traffic. In other words, in example 300, it is assumed that a (0, 3, 6) spacing pattern is employed, and the last partial symbol remains interlace 1 reserved for pilots; similarly, in a wide area traffic region, the pilot should reside on interlace 3 of the first symbol. If a (0, 3, 6) pilot spacing pattern is used, it is possible to impose restrictions on both wide and local blocks such that each of them consists of an odd number of symbols. In this way, it is ensured that the TDM3 pilots follow the same pattern, with odd interlaces being zero outputs. In embodiments that employ a (2, 6) spacing pattern, such a restriction is unnecessary because the TDM3 pilots always contain FDM pilots only on even interlaces. However, in this case, the location of the "cp 1" interleave can be from one waveform boundary to the next. The need to adjust to keep only even interlaces in the TDM3 pilot provides certain advantages for timing synchronization. That is, if the odd, but not even, interlaces are non-zero, the resulting time domain signal is no longer periodic (the second period is the inverse of the first period). This may slightly complicate the demodulation step, however, the overhead is not important and such embodiments may be considered.

Fig. 4 shows an alternative embodiment in which multiple TDM pilot-3 symbols are used. In this embodiment, two additional pilot symbols are employed at the boundary between the local and wide-area data waveforms. This is shown at 410 and 420, where the pilot channel for Local Transition (LTPC) and pilot channel for wide-area transition (WTPC) symbols are displayed as subsets of symbols. Such LTPC and WTPC packets may occur between local and wide-area waveforms in an OFDM transmission, as shown at 420. Generally, LTPC is used to decode the last packet of the local data structure, where the last local symbol may be referred to as local symbol L. Thus, the respective receiver will process three symbol packets, which include partial symbol L, partial symbol L-1, and the respective LTPC, to determine the channel estimate corresponding to the last partial symbol L. If the first wide-area symbol, N, is decoded, the three symbol packets for receiver processing will be WTPC, the first wide-area symbol, N, and the next wide-area symbol, N + 1. It should be understood that more than two TDM3 symbols may also be employed between local and wide-area data boundaries.

The symbol structure for TDM3 (employed for LTPC and WTPC) is similar to that of a general data symbol. This includes that it occupies eight slots and the respective data symbols are all "0" before scrambling, where the interlace is a subset of the carriers and the slots are mapped to the interlace in order to randomize the filling of the interlace. Scrambling of surface acoustic waves (seed) and masks, mapping of slots to interlaces, and modulation symbol energies are similar to those in data symbols. Specifically, the wide area TDM3 symbol-WTPC is scrambled in the surface acoustic wave using the wide area ID, while the local TDM3 symbol-LTPC is scrambled in the surface acoustic wave using both the wide area ID and the local ID. Generally, in one exemplary modem embodiment, the receiver does not need to determine the location of the TDM3 because it uses the FDM pilots as if they were normal data symbols in the respective LTPC or WTPC symbols. However, sending information about the TDM3 location requires very little overhead and can effectively be an upgrade path based on TDM3 for wake-up time tracking and timing synchronization, where TPC symbols corresponding to the following data content are also used for timing synchronization.

For an embodiment with a single TPC symbol on the boundary, and a (0, 3, 6) pilot spacing pattern, fig. 5 shows a possible timing pilot pattern 500. In the following, the processing required in this particular embodiment is described, while a similar approach may be used in different embodiments. In this pattern 500, white boxes represent the interlaces for timing synchronization (in general, the interlaces correspond to the following data content). If the number of symbols in the wide and local areas is a particular form 8n-1, the pattern of white and black pilots on the non-zero interlaces of TDM pilot 3 may remain fixed (e.g., as in fig. 3). As this may not be the case, there may be four different modes 500 that are also used for the example of local-to-wide area conversion. The demodulation technique used by timing synchronization may be slightly different for each of the four different modes in 500.

Consider timing synchronization on the transition from the local to wide-area waveform in the mentioned embodiment with a (0, 3, 6) pilot interval and a single TPC symbol. (this is a more problematic case for timing synchronization, since the wide-area estimated channel is usually the mother set of locally estimated channels). In some wireless networks, timing synchronization is typically based on channel estimation. Since the local pilots represented by "cp 1" in fig. 3 are wrapped by the corresponding local channels, their presence in the received signal does not provide additional information on the wide-area channel. Thus, three pilot interlaces may be used for timing synchronization. This results in a 1536 long wide-area channel estimate. It should be noted that the local pilots are only broadcast from local transmitters and are also specific to the scrambling employed in the local area. Thus, all the receivers can extract the information about the local channel from the local pilots.

For simplicity, consider mode 2 at 510 in FIG. 5, which is consistent with FIG. 3. It can be assumed that two separate symbols are being transmitted linearly, one with wide-area interleaving and the other with only local interleaving, and that they are received after having undergone different channels (wide-area and local), respectively. This is depicted in fig. 5, which is described in more detail below. Since it is of interest to estimate the wide area channel hⁿ(k) The content of the fourth received interlace (denoted by "x") is generally unimportant. Received in this interleaving is effectively linear combiningWherein H₄ ¹And i denotes a fourth interlace of the ith local channel.

Fig. 6 shows an exemplary structure 600 for a received TDM pilot 3 symbol. Note that in fig. 6 non-zero interleaving is considered, i.e. the received OFDM symbol is periodic with two periods of length 2048, which are defined by non-zero interleaving. By sampling one cycle, non-zero interleaving is captured from fig. 3. After appropriate sampling (of the wide-area pilot), 2K-FFT and descrambling, IFFT is performed. Typically, the corresponding steps are performed using a 2K-IFFT, which is implemented as a cascade of four 512-IFFT's, fourThe 512-IFFT is followed by a phase ramp and 4-point IFFT combiner. Consider that the output of the 512-IFFT and phase ramp works on interlace i. If the channel estimation is based on I-pilot interlaces, then a channel of length I.NP, where N is estimated_P512 is the number of pilots per interlace.

In fig. 6, I ═ 3, and this corresponds to a length 1536 channel estimate. The actual channel of interest is of length 4096 (the same length as the useful part of one OFDM symbol). In practice, however, most of the non-zero channel taps are concentrated in a narrow region. In one embodiment, assume that the total number of delay spreads (the area occupied by non-zero channel taps) is at most 768 chips. This non-zero actual channel may occur anywhere between taps O and 4095. The estimate of length 1536 represents an alias version of the actual channel of length 4096. The total channel response of interest (of length 4096) may be divided into eight segments: 0 to 7, where binary k consists of taps 512.k to 512 · (k +1) -1.

In general, the actual non-zero channel content may be located in segments k, k +1 and k +2, modulo 8, while the estimated channel of length 1536 covers only the first three segments. Depending on the segment position of the non-zero channel k, the channel aliases into the three segments of the estimate by means of different aliasing coefficients. In one embodiment, timing synchronization is based on finding the location of non-zero channel content within 4096 channel taps and correlating that information with the currently applicable symbol timing. Since only 1536 sequential taps can be seen, the channel interior can appear differently aliased based on its wide position, some initial assumptions need to be made at regular channel positions (on segments k, k +1, and k + 2). Assuming that some initial timing synchronization has been performed, the non-zero tap is likely to exist in segment (6, 7, 0) or (7, 0, 1). This is shown at 710 of fig. 7. Depending on the timing algorithm used, the occupancy may be limited to (7, 0, 1), as shown at 720 of fig. 7; otherwise, an additional process is performed to determine the occupancy pattern prior to time tracking (also referred to as DMTT, or data pattern time tracking).

In yet another embodiment, the receiver may use only two of the three pilot interlaces in TDM pilot 3, designated for time tracking, and estimate a channel of length 1024. The time domain channel estimation described above can be used for time tracking in a manner very similar to conventional time tracking performed anywhere within a frame. The algorithm for the above-described time tracking is simpler because the aliasing that occurs in this case is the same for all channel segments. An advantage of using a 1536 long channel estimate is that it is more practical to time-track for large time variations.

In the following, a procedure to obtain a channel estimate of length 1536 from three pilot interlaces is described, and it will be appreciated that a similar procedure may be used to obtain a channel estimate of length 1024 using two pilot interlaces of TPC symbols. Returning to FIG. 6, for l ≦ I-1 of 0 ≦ l, h_l(m) represents the l-th part (N) of the estimated channel impulse response_PSample length), where the l-th part refers to content from the l-th segment, which may be confused when considering the estimated channel impulse response. The nth observed tone on the ith interlace is thus given by:

the scaling factor of (a) comes from an implicit N/2-point FFT, which is divided into two steps: np point EFT W_NPFollowed by a 4-point FFT. The last factor in (1) represents the phase ramp, while the factors preceding it correspond to the factors in the l-thAn Np-point FFT operation with an appropriate aliasing factor applied on the channel part. Thus, in N_PPoint IFFT W_NP ^-1And removing the phase ramp Θ from (1)_i ^-1What remains then is a time domain observation consisting of a block of aliased 512-long channel impulse responses. Referring to (1), the confusing observation corresponding to each of the four non-zero interlaces occupied by TDM pilot 3 is given by:

here, the first and second liquid crystal display panels are,andis a vector corresponding to the time-domain and frequency-domain pilot interlace observations, and is as in the l-th of 710 of fig. 7_kEach channel segment is non-empty. For example, in FIG. 7720, give (l)₀，l₁，l₂) (7, 0, 1). 1/2 as a scaling factorAnd (4) obtaining. Note that (2) typically provides four equations, but that in any given example, three of the four possible interlaces are occupied by "time pilots" (the patterns in fig. 5). The final equation in (2) therefore gives three equations with the help of three unknowns. In this case, the unknowns are (h), as shown at 720 of FIG. 7₁，h₀，h₇). The system is solved by inverting the 3 × 3 sub-matrix of the 4-point DFT matrix obtained by removing the i/2 th row (where i is the black staggered index in fig. 5), and holding the column (l)₀，l₁，l₂) mod 4. For example, consider the pattern shown in fig. 7 with hypothetical channel segments (7, 0, 1). A 1536 channel impulse response h (n) as in 720 of fig. 7 is obtained from the observations corresponding to interlaces 0, 2 and 6:

wherein

Fig. 8 shows a block diagram of an exemplary timing synchronization algorithm 800. After applying an appropriate initial offset, the initial sampling time for the 2K-FFT block 810 is determined based on the previous timing. This offset is applied to ensure that the sampled data does represent one period of TDM pilot 3 and does not include time-domain chips from adjacent OFDM symbols. This initial intentional offset is then compensated for when timing corrections are applied. A timing search is then performed on the 1536 length channel estimate to locate non-zero channel content of up to 768 sequential chips in length. In one embodiment, this search is performed by sliding an accumulation window of length 768 over a given channel estimate, and finding the maximum response of the accumulation. In other examples, the decision metric may be based on a linear combination of the accumulated energy over a window and a finite difference applied to the accumulated energy. This metric will typically reach its maximum at or near the first non-zero tap of the significant channel energy. This is also known as the First Arrival Path (FAP) detection algorithm. In yet another embodiment, after computing the accumulated energy curve for channel taps within a sliding window of length 768, the receiver may search for leading and trailing edges of the spatial domain that approach zero characteristic slope of maximum energy. These edge locations can then be converted into the first and last arriving path (FAP and LAP) locations of the channel. This information may then be combined with information associated with the deliberate initial offset to determine the appropriate time offset to apply when processing sequential OFDM symbols.

Some limitations on the algorithm 800 are that the actual delay spread of the upcoming channel does not exceed half the estimated length, 768 in this embodiment, and that the occupied channel segment is known in advance, see fig. 7. Under these assumptions, the timing performance depends on the channel characteristics and on the SNR from the entry to the last 820 of block diagram 8. At this point, each chip of the useful signal, i.e., the channel estimate h (n), has the same power as when all four interlaces of the TDM pilot are used. As for noise, it passes through several modules before reaching this point, and most of them are uniform (in other words, they do not change the noise power). Multiplying by Ω_k，[...] ^-1The noise power will change because the matrix is not uniform. It can be shown, for each possible combination of interlaces i, and the segments l occupied_kCorresponding omega_kThe odd (different) value of (A) is represented by [1, 1, 0.5 ]]Given below. Therefore, at Ω_k ^-1The noise variance on the output 830 of (1+1+4)/3 is increased by 2. The TDM pilot 3 based channel estimate is combined with a static loss of 3dB compared to the channel estimate obtained during the initial fine timing. However, the initial fine timing estimate is 3dB better than the estimates collected at the channel estimation block, and therefore, the fine timing search module 820 is not expected to perform worse than the corresponding module used in data mode timing tracking. Other blocks in the algorithm 800 include an FFT block 840, a descrambling block 850, an IFFT block 860, a rotation matrix selector 870, a phase ramp selector 880, and an active interlace determiner 890.

Fig. 9 shows a pilot symbol procedure 900 for a wireless system. While, for purposes of simplicity of explanation, the methodologies are shown and described as a series or number of acts, it is to be understood and appreciated that the processes described herein are not limited by the order of acts, as some acts may, in accordance with the present invention, occur in different orders and/or concurrently with other acts from that shown and described herein. For example, those skilled in the art will understand and appreciate that a methodology could alternatively be represented as a series of interrelated states or events, such as in a state diagram. Moreover, not all illustrated acts may be required to implement a methodology in accordance with the subject methods disclosed herein.

Proceeding to 910, one or more super frame limits are determined in view of employing additional TDM pilot symbols. As described above, this may include symbol position, slot mapping considerations, scrambling considerations, masking considerations, slot energy considerations, backward compatibility considerations, and impact on the current MAC layer framework. As can be appreciated, the modifications provided at the transmitter of the OFDM broadcast will be considered and explained at the receiver end. At 920, additional TDM pilot restrictions are considered. In an aspect, this may include determining how many additional symbols to add to the set of symbols for legacy TDM1 and TDM 2.

Typically, one additional TDM3 may be included, but more than one symbol may be added to the superframe and associated specification. Other considerations include one or more constraints determined at 910 for the entire superframe structure. At 930, at least one additional TDM pilot symbol is added to the superframe structure. As described above, the first additional pilot generally follows TDM2, with subsequent additional pilots being used for separation between local and wide-area information broadcasts. As can be appreciated, other configurations are possible. When additional pilots have been added to the superframe, timing synchronization, channel estimation, and/or AGC bootstrapping may be performed at 940 on the receivers that obtain the information described above in the OFDM broadcast.

Fig. 10 is an example of a user device 1000 employed in a wireless communication environment in accordance with one or more aspects set forth herein. User device 1000 includes a receiver 1002 that receives a signal from, for instance, a receive antenna (not shown), and performs typical actions thereon (e.g., filters, amplifies, downconverts, etc.) the received signal and digitizes the conditioned signal to obtain samples. A demodulator 1004 can demodulate and provide received pilot symbols to a processor 1006 for channel estimation. Processor 1006 can be a processor dedicated to analyzing information received by receiver 1002 and/or generating information for transmission by a transmitter 1016, a processor that controls one or more components of user device 1000, and/or a processor that both analyzes information received by receiver 1002, generates information for transmission by transmitter 1016, and controls one or more components of user device 1000. User device 1000 can additionally comprise memory 1008 that is operatively coupled to processor 1006.

It will be appreciated that the data store (e.g., memories) components described herein can be either volatile memory or nonvolatile memory, or can include both volatile and nonvolatile memory. By way of example, and not limitation, nonvolatile memory can include Read Only Memory (ROM), Programmable ROM (PROM), Erasable Programmable ROM (EPROM), electrically erasable ROM (EEPROM), or flash memory. Volatile memory can include Random Access Memory (RAM), which acts as external cache memory. By way of example and not limitation, RAM is available in many forms such as Synchronous RAM (SRAM), Dynamic RAM (DRAM), Synchronous DRAM (SDRAM), Double Data Rate SDRAM (DDRSDRAM), Enhanced SDRAM (ESDRAM), Synchlink DRAM (SLDRAM), and Direct Rambus RAM (DRRAM). The memory 1008 of the subject systems and methods is intended to comprise, without being necessarily limited to, these and any other suitable types of memory.

Fig. 11 shows an example system 1100 that includes a base station 1102 with a receiver 1110 that receives signals from one or more user devices 1104 via multiple receive antennas 1106 and a transmitter 1124 that transmits signals to one or more user devices 1104 via transmit antennas 1108. Receiver 1110 can receive information from receive antennas 1106 and is operatively associated with a demodulator 1112, wherein demodulator 1112 demodulates received information. Demodulated symbols are analyzed by a processor 1114, which is similar to processor described above, and which is coupled to a memory 1116.

Fig. 12 illustrates an exemplary wireless communication system 1200. The wireless communication system 1200 depicts one base station and one terminal for sake of brevity. However, it is to be appreciated that the system can include more than one base station and/or more than one terminal, wherein additional base stations and/or terminals can be substantially similar or different for the exemplary base station and terminal described below.

Referring now to fig. 12, on the downlink, at access point 1205, a Transmit (TX) data processor 1210 receives, formats, codes, interleaves, and modulates (or symbol maps) traffic data and provides modulation symbols ("data symbols"). A symbol modulator 1215 receives and processes the data symbols and pilot symbols and provides a stream of symbols. A symbol modulator 1220 multiplexes data and pilot symbols and provides them to a transmitter unit (TMTR) 1220. Each transmit symbol may be a data symbol, a pilot symbol, or a signal value of zero. The pilot symbols may be transmitted continuously in each symbol period. The pilot symbols may be Frequency Division Multiplexed (FDM), Orthogonal Frequency Division Multiplexed (OFDM), Time Division Multiplexed (TDM), Frequency Division Multiplexed (FDM), or Code Division Multiplexed (CDM).

TMTR1220 receives and converts the stream of symbols into one or more analog signals and further conditions (e.g., amplifies, filters, and frequency upconverts) the analog signals to generate a downlink signal suitable for transmission over the wireless channel. The downlink signal is then transmitted via an antenna 1225 to the terminals. At terminal 1230, an antenna 1235 receives the downlink signal and provides a received signal to a receiver unit (RCVR) 1240. Receiver unit 1240 conditions (e.g., filters, amplifies, and frequency downconverts) the received signal and digitizes the conditioned signal to obtain sample values. A symbol demodulator 1245 demodulates and provides received pilot symbols to a processor 1250 for channel estimation. Symbol demodulator 1245 further receives a frequency response estimate for the downlink from processor 1250, performs data demodulation on the received data to obtain data symbol estimates (which are estimates of the transmitted data symbols), and provides the data symbol estimates to an RX data processor 1255, which demodulates (i.e., symbol demaps), deinterleaves, and decodes the data symbol estimates to recover the transmitted traffic data. The processing by symbol demodulator 1245 and RX data processor 1255 is complementary to the processing by symbol modulator 1215 and TX data processor 1210, respectively, at access point 1205.

On the uplink, a TX data processor 1260 processes traffic data and provides data symbols. A symbol modulator 1265 receives and multiplexes the data symbols with pilot symbols, performs modulation, and provides a stream of symbols. A transmitter unit 1270 then receives and processes the stream of symbols to generate an uplink signal, which is transmitted by the antenna 1235 to the access point 1205.

At access point 1205, the uplink signal from terminal 1230 is received by the antenna 1225 and processed by a receiver unit 1275 to obtain sample values. A symbol demodulator 1280 then processes the sample values and provides received pilot symbols and data symbol estimates for the uplink. An RX data processor 1285 processes the data symbol estimates to recover the traffic data transmitted by terminal 1230. A processor 1290 performs channel estimation for each active terminal transmitting on the uplink. Multiple terminals may transmit pilot on the uplink simultaneously on their respective assigned sets of pilot subbands, which may be staggered.

Processors 1290 and 1250 direct (e.g., control, coordinate, manage, etc.) operation at access point 1205 and terminal 1230, respectively. The respective processors 1290 and 1250 can be associated with memory units (not shown) that store program codes and data. Processors 1290 and 1250 can also perform computations to derive frequency and impulse response estimates for the uplink and downlink, respectively.

For a multiple-access system (e.g., FDMA, OFDMA, CDMA, TDMA, etc.), multiple terminals may transmit simultaneously on the uplink. For such systems, the pilot subbands may be shared among different terminals. In the case where the pilot subbands for each terminal span the entire operating band (except, as far as possible, for the band edges), channel estimation techniques may be used. Such a pilot subband structure would be desirable to obtain frequency diversity for the individual terminals. The techniques described herein may be implemented by various means. For example, these techniques may be implemented in hardware, software, or a combination thereof. For a hardware implementation, the processing units used for channel estimation may be implemented within one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof. For software, the implementation can be via modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in memory unit and executed by the processors 1290 and 1250.

For a software implementation, the techniques described herein may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in memory units and executed by processors. The memory unit may be implemented within the processor or external to the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art.

Exemplary embodiments have been included as described above. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the embodiments, but one of ordinary skill in the art may recognize that many further combinations and permutations are possible. Accordingly, these embodiments are intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims. Furthermore, to the extent that the term "includes" or "including" is used in either the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term "comprising" as "comprising" is interpreted when employed as a transitional word in a claim.

Claims (34)

1. A method for timing synchronization at a wireless receiver, comprising:

receiving a data frame having at least one Time Division Multiplexed (TDM) pilot symbol; and

processing the at least one TDM pilot symbol at a transition between the wide area and local waveforms.

2. The method of claim 1, further comprising processing the at least one TDM pilot symbol such that odd interlaces associated with the TDM pilot are set to zero.

3. The method of claim 1, further comprising receiving a data frame comprising Orthogonal Frequency Division Multiplexing (OFDM) symbols.

4. The method of claim 3 further comprising employing at least three of the four even interlaces for time synchronization of the OFDM symbol after the waveform boundary.

5. The method of claim 3, further comprising performing timing synchronization by at least one Fast Fourier Transform (FFT) and at least one Inverse Fast Fourier Transform (IFFT).

6. The method of claim 5 further comprising providing a pilot descrambling component to process data from the FFT component.

7. The method of claim 6 further including determining and applying a phase ramp at interlace i, where i is an integer.

8. The method of claim 7, further comprising determining at least one vector corresponding to time-domain and frequency-domain pilot interlace observations.

9. The method of claim 1, further comprising employing at least one TDM pilot symbol for channel estimation.

10. The method of claim 9, further comprising processing one interlace of the at least one TDM pilot symbol to correspond to a Frequency Division Multiplexing (FDM) pilot interlace of data content before the boundary and processing another interlace of the at least one TDM pilot symbol to correspond to an FDM pilot interlace of data content after the boundary.

11. The method of claim 1, further comprising processing the staggered pattern of the at least one TDM pilot symbol in accordance with a pilot spacing pattern.

12. The method of claim 1, further comprising determining a de-scrambling parameter for the at least one TDM pilot symbol based on a wide area identifier (WID) and a local area identifier (LID).

13. The method of claim 1, further comprising determining data regarding the location of the at least one TDM pilot symbol.

14. A timing synchronization module for a wireless receiver, comprising:

an acquisition component that samples at least one additional pilot symbol for a wireless network receiver; and

at least one decoding component that employs the at least one additional pilot symbol to perform timing synchronization or channel estimation at transitions between wide area and local waveforms.

15. The module of claim 14, further comprising a Fast Fourier Transform (FFT) element associated with said acquisition component.

16. The module of claim 15, wherein said acquisition component receives prior timing position information and applies an initial offset.

17. A module according to claim 16, further comprising a pilot descrambling section for processing data from the FFT components.

18. The module of claim 17 further comprising processing the TDM pilot symbol index to facilitate determining an effective pilot interlace.

19. The module of claim 18, further comprising an Inverse Fast Fourier Transform (IFFT) block to process data from the pilot descrambling component.

20. The module of claim 19, further comprising an observation combining element to process data from the IFFT module.

21. The module of claim 20 further comprising applying a matrix rotation operation to facilitate the observation combining process.

22. The module of claim 21, further comprising phase ramp selection and application to facilitate the observation combining process.

23. The module of claim 22, further comprising a fine timing block to process data from the observation combiner and to determine and perform timing corrections.

24. The module of claim 14, further comprising a machine-readable medium having stored thereon machine-readable instructions to execute the acquisition component or the decoding component.

25. A pilot symbol protocol for a wireless receiver, comprising:

means for decoding at least one Time Division Multiplexed (TDM) pilot symbol at a transition between wide area and local waveforms in a superframe;

means for receiving the superframe in a wireless network; and

means for processing the TDM pilot to perform at least one of channel estimation and timing synchronization.

26. A machine-readable medium having stored thereon and executable instructions thereof, comprising:

generating at least one TDM pilot symbol for each transition between wide-area and local waveforms in the OFDM broadcast;

transmitting the at least one TDM pilot symbol to at least one receiver;

decoding the at least one TDM pilot symbol at the receiver; and

performing timing determination and correction at the receiver based in part on the at least one TDM pilot symbol.

27. The machine-readable medium of claim 26, further comprising performing channel estimation at the receiver.

28. A machine-readable medium having a data structure stored thereon, comprising:

decoding at least one TDM pilot field for each transition between wide and local waveforms;

decomposing the at least one TDM pilot field into one or more interlace fields; and

the interlace field is processed to determine a timing correction for a wireless receiver.

29. The machine-readable medium of claim 28, further comprising processing the interlace field to determine a channel estimate at a receiver.

30. A wireless communications apparatus, comprising:

a memory comprising means for receiving at least one TDM pilot symbol for each transition between wide-area and local waveforms in a superframe; and

at least one processor associated with the receiver that decodes the superframe over the wireless network employs the TDM pilot symbols to determine timing corrections and/or channel estimates for the wireless communication device.

31. A method for channel estimation at a wireless receiver, comprising:

receiving at least one TDM pilot symbol located at a transition between wide area and local waveforms from an OFDM broadcast; and

decoding the at least one TDM pilot symbol to facilitate channel estimation for the wireless receiver.

32. A method for timing synchronization at a wireless receiver, comprising:

receiving a data frame having at least one first Time Division Multiplexed (TDM) pilot symbol associated with a local waveform boundary and at least one second TDM pilot symbol associated with a wide-area waveform boundary; and

processing the first TDM pilot symbols and the second TDM pilot symbols during a data frame.

33. The method of claim 32, further comprising processing a three-symbol packet including a local symbol L, a local symbol L-1, and the first Time Division Multiplexed (TDM) pilot symbol associated with a local waveform to facilitate channel estimation for local symbol L or L-1.

34. The method of claim 32, further comprising processing a three symbol packet including a wide area symbol N, a wide area symbol N-1, and the second Time Division Multiplexed (TDM) pilot symbol associated with a wide area waveform to facilitate channel estimation for either the wide area symbol N or N-1.