WO2009060324A1

WO2009060324A1 - System and method of selectively communicating using ofdm transmissions and single-carrier block transmissions

Info

Publication number: WO2009060324A1
Application number: PCT/IB2008/052460
Authority: WO
Inventors: Dagnachew Birru; Seyed-Alireza Seyedi-Esfahani
Original assignee: Koninklijke Philips Electronics, N.V.
Priority date: 2007-11-07
Filing date: 2008-06-21
Publication date: 2009-05-14

Abstract

A data transmitter transmits data packets comprising a plurality of symbols. The data transmitter maps symbols in at least one of the data packets using a single-carrier transmission format, and maps symbols in at least another of the data packets using a multi-carrier transmission format. The data transmitter maps the symbols using the multi-carrier transmission format when the characteristics of a communication channel over which the data packets are transmitted satisfy a first set of conditions, and maps the symbols using the single-carrier transmission format when the data transmitter determines that the characteristics of the communication channel do not satisfy the first set of conditions. A receiver processes the data packets according to which transmission format was employed in transmission.

Description

SYSTEM AND METHOD OF SELECTIVELY COMMUNICATING USING OFDM TRANSMISSIONS AND SINGLE-CARRIER BLOCK TRANSMISSIONS

This patent application claims the priority benefit under 35 U. S. C. § 119(e) of

U.S. Provisional Patent Application 60/945607, filed on 22 June 2007, the entirety of which is hereby incorporated by reference as if fully set forth herein.

This invention pertains to the field of data communications, and more particularly to a system and method of transmitting a data signal. Data communication systems may be classified in a number of ways according to the transmission schemes that they employ. One classification distinguishes between communication systems which employ a multi-carrier transmission scheme, such as orthogonal frequency division multiplexing (OFDM), and communication systems which employ single-carrier transmission schemes. The choice of which of these types of transmission schemes that a communication system will employ depends on a variety of factors, including characteristics of the communication channel(s), and the requirements of the applications supported by the communication system. For some scenarios, OFDM will be more conducive to meeting those requirements, while other times a single-carrier scheme is a better choice. OFDM is usually a good choice for in situations where the channel is frequency selective, good coding can be deployed, and peak-to-average power ratio is not a significant issue. However, OFDM has disadvantages if the above conditions are not present. For examples, for a multi-gigabit-per-second link in the 60GHz band, transmission power is limited by circuit implementation. Thus, the transmitter has to back-off power in order to accommodate the large peak-to-average power ratio of an OFDM signal. This results in a loss of performance (lower average transmitted power). In addition, the implementation of a powerful decoder for such a high-speed link would typically be expensive, and therefore heavy coding may not be practical. Instead, very weak codes may have to be employed. However, OFDM does not perform well with very weak codes in a frequency selective fading environment.

Adaptive OFDM transmission schemes have been proposed recently and deployed in some wired communication systems. In these adaptive OFDM schemes, the modulation type and power of each carrier is adjusted based on channel conditions. Adaptive OFDM depends on feeding the received channel characteristics back to the transmitter. The transmitter then adjusts the modulation and/or power for each carrier to obtain the best performance for the given channel characteristics. This is commonly known as bit-loading and power loading. The actual details of adaptive OFDM beyond the scope of this patent application. Adaptive OFDM is a good candidate where the communication channel is static, such as is typically the case with a wired communication system. For certain applications such as continuous streaming, the channel may be static for a certain duration. If the protocols are designed to allow continuous streaming, then consecutive packet transmissions may exhibit static behavior. In such case, it may be advantageous to deploy adaptive OFDM.

However, adaptive OFDM has not been employed widely in wireless communication systems. One reason is that most common wireless communication environments and media access protocols do not result in, or guarantee, static channel characteristics. A single-carrier transmission scheme, on the other hand, in general has a lower peak-to-average-power ratio than a typical OFDM system. Furthermore, its performance is typically better than that of OFDM in a frequency-selective channel where weakly coded data is transmitted. However, a standard single-carrier system typically requires an equalization scheme that is relatively expensive to implement. To ease the equalization requirement, single-carrier block single transmission (SCBT) schemes have been proposed recently. These SCBT schemes insert either zeros or a cyclic prefix to a block of data, just as is done in a conventional OFDM system.

So it is seen that OFDM and SCBT each can provide certain advantages under certain channel conditions, and can present certain disadvantages under other channel conditions.

Accordingly, it would be desirable to provide a transmission scheme that can realize the benefits of OFDM in situations where OFDM transmission is advantageous, and can realize the benefits of a single-carrier transmission scheme in situations where single- carrier transmission is advantageous. In one aspect of the invention, a data transmission system includes: a first symbol mapper adapted to receive bits and map the bits into first symbols using a single-carrier transmission format; a second symbol mapper adapted to receive the bits and map the bits into second symbols using a multi-carrier transmission format; and transmission signal format selection means for selecting symbols among the first symbols output from the first symbol mapper and the second symbols output from the second symbol mapper and for providing the selected symbols to be transmitted.

In another aspect of the invention, a data receiver comprises: a frequency domain transformer adapted to receive an input signal comprising a plurality of symbols and to transform the input signal into a frequency domain; a channel equalizer for equalizing the transformed signal according to an estimated of a communication channel over which the signal was received and to output a first signal; an inverse frequency domain transformer adapted to receive the first signal, to transform the first signal to a time domain, and to output a second signal; format selection means for selecting between the first signal and the second signal and to output a selected signal; and a demapper adapted to demap the selected signal to output a series of bits.

In yet another aspect of the invention, a method is provided for transmitting data packets comprising a plurality of symbols from a data transmitter. The method includes the data transmitter mapping symbols in at least a first one of the data packets using a single-carrier transmission format, and mapping symbols in at least a second one of the data packets using a multi-carrier transmission format. The first and second data packets are transmitted using at least one common antenna.

FIG. 1 is a functional block diagram of one embodiment of a data transmitter. FIG. 2 is one embodiment of a packet structure that may be employed for data packets transmitted by a data transmitter.

FIG. 3 is a functional block diagram of one embodiment of a data receiver.

In the following detailed description, for purposes of explanation and not limitation, example embodiments disclosing specific details are set forth in order to provide a thorough understanding of an embodiment according to the present teachings. However, it will be apparent to one having ordinary skill in the art having had the benefit of the present disclosure that other embodiments according to the present teachings that depart from the specific details disclosed herein remain within the scope of the appended claims. Moreover, descriptions of well-known apparati and methods may be omitted so as to not obscure the description of the example embodiments. Such methods and apparati are clearly within the scope of the present teachings.

FIG. 1 is a functional block diagram of one embodiment of a data transmitter 100. As will be appreciated by those skilled in the art, the various functions shown in FIG. 1 may be physically implemented using a software-controlled microprocessor, hard-wired logic circuits, or a combination thereof. Also, while the functional blocks are illustrated as being segregated in FIG. 1 for explanation purposes, they may be combined in any physical implementation. Data transmitter 100 includes coder/interleaver 105, transmission signal format selection means 110, first symbol mapper 120, second symbol mapper 130, pilot tone generator 140, preamble & channel equalization (CE) sequence generator 145, guard interval inserter 150, upconverter 160, high frequency transmit amplifier 170, and antenna system 180. Coder/interleaver 105 includes an error correction encoder and a data interleaver.

The error correction coder may encode data bits to be communicated with a convolutional code, a block code, or some combination thereof including a concatenated code.

Transmission signal format selection means 110 includes a demultiplexer or switch 112 for selectively providing coded and interleaved data to a selected one of the first and second symbol mappers 120/130, and further includes a multiplexer or switch 114 for selectively providing mapped data symbols from the selected one of the first and second symbol mappers 120/130 to guard interval inserter 150. In an alternative embodiment, demultiplexer or switch 112 may be omitted and the coded and interleaved bits may be provided to both the first and second symbol mappers 120/130. As noted above, depending on the data rates employed and the development of processors operating at higher and higher speeds, the various "parts" shown in FIG. 1 may be physically implemented using a software-controlled microprocessor, hard-wired logic circuits, or a combination thereof. In that case, transmission signal format selection means 110 may comprise a branch in a software routine that determines whether a processor maps the coded and interleaved data using a single-carrier transmission format (symbol mapper 120), or using a multi-carrier transmission format (symbol mapper 130).

First symbol mapper 120 maps bits to symbols according to a single-carrier format. For example, first symbol mapper 120 may employ quadraphase shift keying (QPSK) M- quadrature amplitude modulation (M-QAM), etc. Second symbol mapper 130 includes a serial-to-parallel converter 132, an adaptive modulator 134, a time domain transformer (e.g., an inverse fast Fourier transformer) 136, and a parallel-to-serial converter 138. Second symbol mapper 130 maps bits to symbols according to a multi-carrier format. Beneficially, second symbol mapper 130 maps bits to symbols using adaptive orthogonal frequency division multiplexing (adaptive-OFDM).

Pilot tone generator 140 generates pilot tones which may be used to facilitate receiver detection of the transmitted signal. In some embodiments, pilot tone generator 140 may be omitted. Preamble & CE sequence generator 145 generates a sequence that appears at the start of each data packet transmitted by data transmitter 100. In one embodiment, preamble & CE sequence generator 145 generates a preamble sequence, and a sequence (e.g., a training sequence) used for channel equalization. FIG. 2 shows one exemplary embodiment of a data packet 200 including a preamble, a channel equalization sequence, and a packet header, which will be described in greater detail below. In one embodiment, the preamble includes an automatic gain control (AGC) sequence and a synchronization sequence for use by a data receiver.

In one embodiment as shown in FIG. 1, preamble & CE sequence generator 145 supplies bits for the preamble and CE sequences to first and second symbol mappers 120/130 (e.g., via transmission signal format selection means 110), one of which is selected by signal format selection means 110 to be used for transmission. Alternatively, as illustrated in dashed lines in FIG. 1, preamble & CE sequence generator 145 may generate symbols for the preamble & CE sequences directly and provide those symbols for transmission via transmission signal format selection means 110. In that case, beneficially preamble & CE sequence generator 145 generates symbols using either the single-carrier transmission format of first symbol mapper 120 or the multi-carrier transmission format of second symbol mapper 130. Also, a header generator (not shown in FIG. 1) supplies header bits to coder/interleaver 105 for each data packet and these bits are mapped by a selected one of the first and second symbol mappers 120/130 using a same transmission format as is employed for the preamble and CE sequences.

In one embodiment, upconverter 160 includes an upsampler, a filter, and a digital- to-analog converter. Other convenient arrangements may be employed.

Antenna system 180 may include one antenna, or may include multiple antennas for example for a space-division multiple access (SDMA) scheme. In general, data transmitter 100 may be included in a communication device that also includes a data receiver and a processor. The communication device may include other elements that provide functionality to the communication device.

Operationally, data transmitter 100 functions generally as follows. Beneficially, data transmitter 100 provides a flexible transmission scheme where either a multi-carrier transmission format (e.g., adaptive OFDM) or a single-carrier transmission format (e.g., SCBT) can be selected for each data packet based on the communication channel and operating conditions. Also beneficially, particularly when adaptive OFDM and SCBT are employed, the two schemes can be seamlessly implemented in both data transmitter 100 and a data receiver receiving the transmitted signal, as will be discussed further below.

Coder/interleaver 105 receives data (including typically a packet header), encodes the data with an error correction code, and interleaves the encoded data. The data may be encoded with a convolutional code, a block code, or some combination thereof including a concatenated code.

Then, the encoded and interleaved data bits are converted to symbols using one of two transmission formats: a single-carrier transmission format (e.g., SCBT), and a multi- carrier transmission format (e.g., OFDM). Selection of which transmission format is employed may be performed as follows.

Data transmitter 100 transmits data to one or more data receivers over a communication channel. Beneficially, information regarding the communication channel is available to a communication device including data transmitter 100. In one embodiment, channel information is received by a data receiver in the communication device that includes data transmitter 100 from a transmitter of another communication device that receives the data signal transmitted by data transmitter 100. Alternatively, a data receiver in the communication device including data transmitter 100 may determine communication channel conditions based on one or more signal(s) that it receives from one or more other communication devices. However the communication channel information is obtained, it may be provided to a processor (not shown in FIG. 1) which controls operation of data transmitter 100. When the characteristics of the communication channel satisfy a predefined set of conditions, then data transmitter 100 maps the symbols using the multi-carrier transmission format. However, when the data transmitter determines that the characteristics of the communication channel do not satisfy the predefined set of conditions, then data transmitter 100 maps the symbols using the single-carrier transmission format. Beneficially, the predefined set of conditions identifies situations in which the communication channel characteristics are expected to be relatively static. More specifically, when the communication channel conditions are determined to be static, then a processor (not shown in FIG. 1) controls data transmitter 100 to select the multi-carrier transmission format. In that case, data transmitter 100 transmits symbols mapped by second symbol mapper 130. In one embodiment, the processor controls transmission signal format selection means 110 (including at least multiplexer 114) to select symbols mapped by second symbol mapper 130, and provides the selected symbols to be transmitted via antenna 180. Also, when the communication channel exhibits frequency selectivity, then data transmitter 100 may use this information to change the modulation and power of each carrier of the OFDM signal. Alternatively, when the channel conditions are determined to show some dynamic behavior (e.g., Doppler, people moving, the protocol does not guarantee consecutive packet transmissions thereby increasing the chance of channel changes), then the processor controls data transmitter 100 to select the SCBT transmission format. In that case, data transmitter 100 transmits symbols mapped by first symbol mapper 120. In one embodiment, the processor controls transmission signal format selection means 110

(including at least multiplexer 114) to select symbols mapped by first symbol mapper 120, and provides the selected symbols to be transmitted via antenna 180.

Beneficially, the size of the data blocks employed in the OFDM transmission format and the SCBT transmission format are the same, and the data sampling is also the same.

In either event, the selected symbols are then provided to the rest of the data transmission chain, including guard interval inserter 150, upconverter 160, high frequency transmit amplifier 170, and antenna system 180.

Guard signal inserter 150 inserts either a cyclic prefix or a sequence of zeros in front of each block of symbols to be transmitted to create a gap interval between each block. Beneficially, this can ease channel equalization requirements at the data receiver. For example, in one embodiment 128 data symbols may be transmitted in each block, and the 32 symbols may be pre-pended to the front of each block for transmission. Alternatively, 32 zeros may be placed in front of each block of 128 symbols before transmission.

The resulting blocks of symbols are upconverted, amplified, and transmitted by antenna system 180. Because data transmitter 100 transmits data at any given time according to a selected one of two possible data transmission formats, any data receiver that is to receive the data should have some means of knowing which data transmission format is being employed so that it can be properly configured to receive the data. Beneficially, data transmitter 100 communicates this information in a header of a data packet that it transmits.

FIG. 2 is one embodiment of a structure of a data packet 200 that may be employed in a data transmission of a communication transmitter.

Data packet 200 includes a preamble sequence 210, a channel equalization sequence 220, a packet header 230, one or more data segments 240-z, and one or more pilot tone segments 250-z interleaved between data segments 240-z.

Preamble sequence 210 includes an automatic gain control (AGC) sequence and a synchronization sequence for use by a data receiver. Beneficially, this preamble consists of repetition of a certain length sequence. Channel equalization sequence 220 is a predetermined sequence that is designed to facilitate channel equalization by a data receiver.

Header 230 includes information about the data to be transmitted in the data packet, such as number of sate segments, coding type, etc.

In order to facilitate initial communication, a first portion of each data packet comprising preamble sequence 210, channel equalization sequence 220, and packet header 230 is transmitted using a common data transmission scheme. This common data transmission scheme is known a priori to every data transmitter and data receiver and is fixed. Beneficially, the common data transmission scheme employs either the same single- carrier transmission format employed by first symbol mapper 120, or the multi-carrier transmission format employed by second symbol mapper 130. In that case, the symbols for the first portion of the data packet may be generated by a corresponding one of the first and data symbol mappers 120/130. Alternatively, preamble & CE sequence generator 145 may generate the symbols for the preamble and CE sequences directly.

Beneficially, header 230 includes one or more bits which identify whether the symbols in the second portion of the data packet are mapped according to the single-carrier transmission format (e.g., SCBT), or whether the symbols in the second portion of the data packet are mapped according to the multi-carrier transmission format (e.g., adaptive OFDM). In one embodiment, a pilot sequence 250-z is inserted in-between the data segments 240-z to help a data receiver track clock/frequency offsets and channel changes.

FIG. 3 is a functional block diagram of one embodiment of a data receiver 300.

Data receiver 300 includes a synchronization and guard band removal block 310, a frequency domain transformer 320, a channel equalizer 330, a channel estimator 335, an inverse frequency domain transformer 340, a format selection means 350, a demapper 360, and a decoder/deinterleaver 370.

In one embodiment, frequency domain transformer 320 performs a fast Fourier Transform (FFT). However, other transforms may be performed instead. Also in one embodiment, inverse frequency domain transformer 340 performs an inverse fast Fourier Transform (IFFT). Again, however, other transforms may be performed instead. Furthermore, in one embodiment format selection means 350 includes a demultiplexer or switch. Although not shown in FIG. 3, in an alternate embodiment, format selection means 350 may also include a multiplexer or switch for selectively providing the output of channel equalizer 330 to one of inverse frequency domain transformer 340 and demapper 360. Decoder/deinterleaver 370 includes an error correction decoder and a data deinterleaver. The error correction decoder may decode data bits according to a predefined convolutional code, block code, or some combination thereof including a concatenated code. In general, data receiver 300 may be included in a communication device that also includes a data transmitter and a processor. The communication device may include other elements that provide functionality to the communication device.

Operationally, data receiver 300 functions generally as follows.

Synchronization and guard band removal block 310 receives symbols from a receive antenna system (which may include multiple antennas for space diversity) and downconverter block (not shown in FIG. 3).

Frequency domain transformer 320 receives an input signal from synchronization and guard band removal block 310, comprising a plurality of symbols, and transforms the input signal to the frequency domain. Channel equalizer 330 equalizes the transformed signal according to an estimation of the communication channel over which the signal was received, and outputs a first signal. The channel estimation may be obtained from channel estimation block 335. Channel estimation block 335 may estimate the channel using a received channel equalization sequence such as channel equalization sequence 220 in packet 200.

Inverse frequency domain transformer 340 receives the first signal, transforms the first mapped signal to the time domain, and outputs a second signal. Format selection means 350 selects between the first signal and the second signal and outputs the selected signal to demapper 360. Beneficially, format selection means 350 selects one of the first and second signals for the first portion of each data packet (e.g., preamble, CE sequence, and header) according to a predetermined transmission format for that part of the data packet. Then, using one or more bits in the preamble, data receiver 300 is able to determine which of the two transmission formats was used for the second portion of the data packet having the data payload.

When the data transmission format is a single-carrier transmission format (e.g., SCBT), then data receiver 300 controls format selection means 350 to select the second signal output by inverse frequency domain transformer 340 and to provide the selected signal to demapper 360. Otherwise, when the data transmission format is a multi-carrier transmission format (e.g., adaptive OFDM), then data receiver 300 controls format selection means 350 to select the first signal output by channel equalizer 330 and to provide the selected signal to demapper 360.

Demapper 360 demaps symbols from the selected signal to output a series of bits. Finally, decoder/deinterleaver 370 applies error correction decoding to the demapped bits, and deinterleaves the corrected bits to produce an output signal.

Beneficially, data receiver 300 provides a very efficient implementation for receiving signals having the two different transmission formats: a single-carrier transmission format, and a multi-carrier transmission format. Most of the blocks are common to the two formats, while inverse frequency domain transformer 340 is employed when the SCBT mode is utilized.

While preferred embodiments are disclosed herein, many variations are possible which remain within the concept and scope of the invention. Such variations would become clear to one of ordinary skill in the art after inspection of the specification, drawings and claims herein. The invention therefore is not to be restricted except within the spirit and scope of the appended claims.

Claims

1. A data transmission system (100), comprising: a first symbol mapper (120) adapted to receive bits and map the bits into first symbols using a single-carrier transmission format; a second symbol mapper (130) adapted to receive the bits and map the bits into second symbols using a multi-carrier transmission format; and transmission signal format selection means (110) for selecting symbols among the first symbols output from the first symbol mapper (120) and the second symbols output from the second symbol mapper (130) and for providing the selected symbols to be transmitted.

2. The data transmission system (100) of claim 1, further comprising a data encoder and an interleaver (105) for encoding and interleaving the bits provided to the first and second symbol mappers (120/130).

3. The data transmission system (100) of claim 1, wherein the data transmission system (100) is adapted to transmit a plurality of data packets (200) each including a first portion (210/220/230) and a second portion (240-i) sequentially following the first portion (210/220/230), wherein all symbols in the first portion (210/220/230) of each data packet (200) are output by a same one of the first and second symbol mappers (120/130), and wherein symbols in the second portion (240-i) of at least one of the data packets (200) are output from the first symbol mapper (120), and symbols in the second portion of at least another of the data packets are output from the second symbol mapper (130).

4. The data transmission system (100) of claim 3, wherein the first portion (210/220/230) of each data packet (200) includes a header (230), the header (230) of each data packet (200) further including one or more bits that indicate whether the symbols in the second portion (240-z) of the data packet (200) are mapped according to the single- carrier transmission format (120), or whether the symbols in the second portion (240-z) of the data packet (200) are mapped according to the multi-carrier transmission format (130).

5. The data transmission system (100) of claim 1, wherein the second symbol mapper (130) includes an adaptive orthogonal frequency division multiplexing (OFDM) modulator.

6. The data transmission system (100) of claim 1, wherein the transmission signal format selection means (110) comprises at least one of a multiplexer and a switch.

7. The data transmission system (100) of claim 1, wherein the first symbol mapper (120) and the second symbol mapper (130) are each adapted to process the received bits in blocks, wherein a size of the block for the first symbol mapper (120) is the same as the size of a block for the second symbol mapper (130), and wherein one of a predetermined cyclic prefix or a predetermined number of zeros is inserted before each block of the selected symbols prior to transmission.

8. The data transmission system (100) of claim 1, further comprising a gap interval inserter (150) adapted to receive the selected symbols and to insert one of a predetermined cyclic prefix or a predetermined number of zeros before each block of the selected symbols prior to transmission.

9. A data receiver (300) adapted to receive data packets (200) comprising a plurality of symbols, wherein in a first portion (210/220/230) of each data packet (200) symbols are mapped according to a fixed transmission format, and in a second portion (240-z) of each data packet (200) symbols are mapped according to a selected one a first transmission format (120) and a second transmission format (130), wherein the data receiver (300) extracts from the first portion (210/220/230) of each data packet (200) information identifying which one of the first transmission format (120) and second transmission format (130) are employed in the second portion (240-z) of the data packet (200), and wherein the receiver (300) detects data in the second portion (240-z) of the data packet (200) according to the identified transmission format.

10. The data receiver (300) of claim 9, comprising: a frequency domain transformer (320) adapted to receive an input signal comprising the plurality of symbols and to transform the input signal into a frequency domain; a channel equalizer (330) for equalizing the transformed signal according to an estimation of a communication channel over which the signal was received and to output a first signal; an inverse frequency domain transformer (340) adapted to receive the first signal, to transform the first signal to a time domain, and to output a second signal; format selection means (350) for selecting between the first signal and the second signal and to output a selected signal; and a demapper (360) adapted to demap the selected signal to output a series of bits.

11. The data receiver (300) of claim 10, further comprising a guard interval remover (310) adapted to remove symbols in a guard interval from a received signal and to provide the input signal to the frequency domain transformer (320).

12. The data receiver (300) of claim 10, further comprising a data decoder and a deinterleaver (370) for decoding and deinterleaving the series of bits from the demapper (360).

13. The data receiver (300) of claim 10, wherein for the first portion (210/220/230) of each data packet (200) the format selection means (350) always selects a same one of the first signal and the second signal, and wherein for the second portion (240-z) of at least one of the data packets (200) the format selection means (350) selects the first signal, and for the second portion (240-z) of at least another of the data packets (200) the format selection means (350) selects the second signal.

14. The data receiver (300) of claim 13, wherein the first portion (210/220/230) of each data packet (200) includes a header (230), the header (230) of each data packet (200) further including one or more bits that indicate whether the symbols in the second portion (240-z) of the data packet (200) are mapped according to the single-carrier transmission format, or whether the symbols in the second portion (240-z) of the data packet (200) are mapped according to the multi-carrier transmission format, and wherein the data receiver (300) is adapted to detect the one or more bits in the header (230) and to control the format selection means (350) in accordance with the one or more bits in the header (230).

15. The data receiver (300) of claim 10, the format selection means (350) comprises at least one of a multiplexer and a switch.

16. A method of transmitting data packets (200) comprising a plurality of symbols from a data transmitter (100), comprising: the data transmitter (100) mapping symbols in at least a first one of the data packets (200) using a single-carrier transmission format (120); the data transmitter mapping symbols in at least a second one of the data packets (200) using a multi-carrier transmission format (130); transmitting the first and second data packets (200) using at least one common antenna (180).

17. The method of claim 16, wherein the data transmitter (100) maps the symbols using the multi-carrier transmission format (130) when the data transmitter (100) determines that characteristics of a communication channel over which the data packets (200) are transmitted satisfy a first set of conditions, and wherein the data transmitter (100) maps the symbols using the single-carrier transmission format (120) when the data transmitter (100) determines that the characteristics of the communication channel do not satisfy the first set of conditions.

18. The method of claim 16, wherein the single-carrier transmission format (120) is a single-carrier block single transmission (SCBT) format, and wherein the multi-carrier transmission format (130) is an orthogonal frequency division multiplex (OFDM) format.

19. The method of claim 16, wherein each data packet (200) includes a first portion (210/220/230) and a second portion (240-z), further comprising: the data transmitter (100) mapping symbols in the first portion (210/220/230) of each data packet (200) using a same one of the single-carrier transmission format (120) or the multi-carrier transmission format (130); and the data transmitter (100) mapping symbols in the second portion (240-z) of a first one of the data packets (2000 using the single-carrier transmission format (120).

20. The method of claim 19, wherein the first portion (210/220/230) of each data packet (200) includes a header (230), the header (230) of each data packet (200) further including one or more bits that indicate whether the symbols in the second portion (240-z) of the data packet (200) are mapped according to the single-carrier transmission format (120), or whether the symbols in the second portion (240-z) of the data packet (200) are mapped according to the multi-carrier transmission format (130).

21. The method of claim 16, wherein each data packet (200) includes a plurality of blocks of symbols, the method further comprising inserting one of a predetermined cyclic prefix or a predetermined number of zeros is inserted before each block of the selected symbols prior to transmission.

22. A method of transmitting data packets comprising a plurality of symbols from a data transmitter (100), comprising: the data transmitter (100) transmitting in a first portion (210/220/230) of each data packet (200) symbols that are mapped according to a fixed transmission format; and the data transmitter (100) transmitting in a second portion (240-z) of each data packet (200) symbols that are mapped according to a selected one a first transmission format (120) and a second transmission format (130), wherein at least one symbol in the first portion (210/220/230) of the data packet (200) includes information identifying which one of the first transmission format (120) and second transmission format (130) are employed in the second portion (240-z) of the data packet (200).

23. The method of claim 22, wherein the first transmission format is a single-carrier transmission format (120) and the second transmission format is a multi-carrier transmission format (130).

24. The method of claim 23, wherein the single-carrier transmission format (120) is a single-carrier block single transmission (SCBT) format, and wherein the multi-carrier transmission format (130) is an orthogonal frequency division multiplex (OFDM) format.

25. The method of claim 23, wherein the fixed transmission format corresponds to one of the first transmission format (120) and second transmission format (130).