Space-time coding for UMTS. Performance evaluation in combination with convolutional and turbo coding

Space-time codes provide both diversity and coding gain when using multiple transmit antennas to increase spectral efficiency over wireless communications systems. Space-time block codes have already been included in the standardization process of UMTS in conjunction with conventional channel codes (convolutional and turbo codes). We discuss different encoding and decoding strategies when transmit diversity is combined with conventional channel codes, and present simulations results for the TDD and FDD modes of UTRA.Peer ReviewedPostprint (published version

Turbo-Detected Unequal Protection MPEG-4 Wireless Video Telephony using Multi-Level Coding, Trellis Coded Modulation and Space-Time Trellis Coding

Most multimedia source signals are capable of tolerating lossy, rather than lossless delivery to the human eye, ear and other human sensors. The corresponding lossy and preferably low-delay multimedia source codecs however exhibit unequal error sensitivity, which is not the case for Shannon’s ideal entropy codec. This paper proposes a jointly optimised turbo transceiver design capable of providing unequal error protection for MPEG-4 coding aided wireless video telephony. The transceiver investigated consists of space-time trellis coding (STTC) invoked for the sake of mitigating the effects of fading, in addition to bandwidth efficient trellis coded modulation or bit-interleaved coded modulation, combined with a multi-level coding scheme employing either two different-rate non-systematic convolutional codes (NSCs) or two recursive systematic convolutional codes for yielding a twin-class unequal-protection. A single-class protection based benchmark scheme combining STTC and NSC is used for comparison with the unequal-protection scheme advocated. The video performance of the various schemes is evaluated when communicating over uncorrelated Rayleigh fading channels. It was found that the proposed scheme requires about 2.8 dBs lower transmit power than the benchmark scheme in the context of the MPEG-4 videophone transceiver at a similar decoding complexity

Performance analysis of space-time codes with channel information errors

Many space-time codes (STC) have been proposed to enhance the performance of wireless communications in flat fading channels. All of them rely on the knowledge of the channel, and are hence affected by the channel estimation errors. Most previous research on STC performance evaluation assume perfect channel information. In this paper, we investigate STC robustness under imperfect channel knowledge. We first define the concept of "closeness" by comparing the BER under channel estimation errors with that of perfect channel knowledge, aiming to characterize STC performance degradation due to imperfect channel knowledge. Then the robustness of STC can be compared by their "closeness" to perfect results. In our computer simulations, we apply the same channel estimator to different STCs in Orthogonal Frequency Division Multiplexing (OFDM) communication systems. We find that for systems with two and three transmit antennas, the space time block codes (STBC) are always more robust to channel estimation errors than space time trellis codes (STTC). With the increase of receive diversity, all STCs become more robust to the channel estimation errors. For STTC, as the number of trellis states increases, the codes become less robust to the channel estimation errors. We also compare the BER performance of STC in the presence of channel estimation errors. For the two-transmit-antenna system, the performance of STBC is always better than that of the 4-state STTC, but is always worse than 16-state STTC. For systems with three transmit antennas, the BER performance of STTC is much better than that of STBC. © 2004 IEEE.published_or_final_versio

Robustness of space-time codes in the presence of channel estimation errors in OFDM systems

Many space-time codes (STC) have been proposed to enhance the performance of wireless communications in flat fading channels. All of them rely on the knowledge of the channel, and are hence affected by the channel estimation errors. In this paper, we investigate STC robustness under imperfect channel knowledge. We first define the concept of "closeness" by comparing the BER under channel estimation errors with that under perfect channel knowledge, aiming to characterize STC performance degradation due to imperfect channel knowledge. Then the robustness of STC can be compared by their "closeness" to perfect results. We find that for systems with two and three transmit antennas, the space time block codes (STBC) are always more robust to channel estimation errors than space time trellis codes (STTC). With the increase of receive diversity, all STCs become more robust to the channel estimation errors. For STTC, as the number of trellis states increases, the codes become less robust to the channel estimation errors. We also compare the BER performance of STC in the presence of channel estimation errors. For the two-transmit-antenna system, the performance of STBC is always better than that of the 4-state STTC, but is always worse than 16-state STTC. For systems with three transmit antennas, the BER performance of STTC is much better than that of STBC.published_or_final_versio

Space-Time Codes Concatenated with Turbo Codes over Fading Channels

The uses of space-time code (STC) and iterative processing have enabled robust communications over fading channels at previously unachievable signal-to-noise ratios. Maintaining desired transmission rate while improving the diversity from STC is challenging, and the performance of the STC suffers considerably due to lack of channel state information (CSI). This dissertation research addresses issues of considerable importance in the design of STC with emphasis on efficient concatenation of channel coding and STC with theoretical bound derivation of the proposed schemes, iterative space-time trellis coding (STTC), and differential space-time codes. First, we concatenate space-time block code (STBC) with turbo code for improving diversity gain as well as coding gain. Proper soft-information sharing is indispensable to the iterative decoding process. We derive the required soft outputs from STBC decoders for passing to outer turbo code. Traditionally, the performance of STBC schemes has been evaluated under perfect channel estimation. For fast time-varying channel, obtaining the CSI is tedious if not impossible. We introduce a scheme of calculating the CSI at the receiver from the received signal without the explicit channel estimation. The encoder of STTC, which is generally decoded using Viterbi like algorithm, is based on a trellis structure. This trellis structure provides an inherent advantage for the STTC scheme that an iterative decoding is feasible with the minimal addition computational complexity. An iteratively decoded space-time trellis coding (ISTTC) is proposed in this dissertation, where the STTC schemes are used as constituent codes of turbo code. Then, the performance upper bound of the proposed ISTTC is derived. Finally, for implementing STBC without channel estimation and maintaining trans- mission rate, we concatenate differential space-time block codes (DSTBC) with ISTTC. The serial concatenation of DSTBC or STBC with ISTTC offers improving performance, even without an outer channel code. These schemes reduce the system complexity com- pared to the standalone ISTTC and increase the transmission rate under the same SNR condition. Detailed design procedures of these proposed schemes are analyzed

Performance comparison of differential space-time signalling schemes for OFDM systems

Differential transmit diversity is an attractive alternative to its coherent counterpart, especially for multiple antenna systems where channel estimation is more difficult to attain compared to that of single antenna systems. In this paper we compare two different types of differential transmit diversity techniques for OFDM based transmissions. The first technique uses differential space-time block codes (DSTBC) from orthogonal designs and the second uses the differential cyclic delay diversity (DCDD). The results compare the bit error performance for several transmit antenna configurations. The results show that DCDD offers a very close performance to that of DSTBC, with the advantage of a simplified receiver structure

Performance Analysis Of A Cellular System Using C-Ofdm Techniques

The basic idea of COFDM is to split the modulation samples of incoming data stream onto a large number of carriers instead of modulating a unique carrier. Therefore, COFDM is an effective technique for combating multi-path fading and for highbit- rate transmission over wireless channel. In a single carrier system a frequency Selective fading can cause the entire transmission link to fail, but in an COFDM multi carrier system, only a small percentage of the sub-carriers will be corrupted. Frequency and time interleaving in conjunction with forward error correction coding can then be used to correct for erroneous subcarriers. The background information with the aim to provide an intuitive explanation of our research motivation. C-OFDM is the modulation scheme of choice , as enshrined in International standard for all forms of digital broadcasting both audio and video and including satellite, terrestrial, and cable. In the existing standard the “coding” referred to consists of an inner convolutional code concatenated with an outer R-S code; here in this thesis, we replace the inner code with the coding like space time trellis code for analysi

Distributed convolutional-coded differential space-time block coding for cooperative communications

A low complexity distributed coding scheme is proposed for communications over Rayleigh fading channels. Convolutional Coding (CC) assisted Differential Phase-Shift Keying (DPSK) modulation is employed at the source node for conveying the source signals to two relay nodes as well as to the destination node during the first transmission period. Iterative detection exchanging extrinsic information between the DPSK demapper and CC decoder is carried out at each relay node in order to recover the source signals. Then, the CC-encoded bits are re-encoded by the two relays to generate Differential Space-Time Block Coding (DSTBC) symbols for transmission to the destination node during the second transmission period. At the destination node, iterative decoding exchanging extrinsic information is invoked between the DPSK demapper and the concatenated CC-DSTBC decoder, where the later is viewed as a single amalgamated decoder. The relay and destination nodes do not have to estimate the channel’s fading coefficients due to the employment of DPSK and DSTBC schemes. Our design requires only two decoding iterations between the DPSK and CC decoders at each relay in order to further reduce the complexity of the relay nodes. Our distributed coding scheme assisted by two low-complexity relay nodes outperforms the non-cooperative benchmarker scheme by about 8 dBs, when aiming for a bit error ratio of 10-5

Design and analysis of space-time block and trellis coding schemes for single-band UWB communications systems

Ultra Wide-Band (UWB) technology has recently attracted much research interest due to its appealing features in short-range mobile communications. These features include high-data rates, low power consumption, multiple-access communications and precise positioning capabilities. Space-Time Coding (STC) techniques, such as block coding and trellis coding, are known to be simple and practical ways to increase both the spectral efficiency and the capacity in wireless communications. The the- sis aims at designing robust and efficient space-time coding schemes well adapted to single-band UWB signalling. Thus, this work incorporates a fine analysis of a stan- dard Single Input Single Output (SISO) single-band UWB system, scrutinising every important aspect of this system including transceiver structure, channel modelling, multiple-access techniques and detection process. Research also leads to the deriva- tion of a novel closed-form approximation for the average probability of bit-error for single-band UWB systems. This in-depth study highlights drawbacks inherent to UWB systems such as time-jitter effects or rake-receiver complexity and proposes schemes that benefit from spatial diversity to mitigate these problems. Thus, the thesis concentrates on the design of new multiple-antenna space-time coding systems tailored for UWB communications. As a result, this work derives and generates gen- eralised full-rate space-time block codes based on orthogonal pulses to capture both spatial and multipath diversities. Space-time trellis coded modulation is then revis- ited to further improve the spectral efficiency limit and to deliver the high-data rates promised by UWB technology. A new version of space-time trellis coding is developed for the peculiar UWB signalling structure. Finally, thanks to a novel closed-form ap- proximation, a theoretical comparison is undertaken between any SISO-UWB system and the multiple antenna UWB systems proposed in this thesis. The results clearly underline the impact of STC on a single-band UWB system in terms of enhanced robustness against timing-jitter effects, higher spectral efficiency and capacity im- provement. These advantages are finally confirmed through the numerical evaluation of the error-rate performance.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Space-time coding for mimo rayleigh fading systems

Ph.DDOCTOR OF PHILOSOPH