Single Carrier Frequency-Domain Equalization with Transmit Diversity over Mobile Multipath Channels

This letter addresses the application of Linear Dispersion Codes (LDC) in space and frequency domains in Single Carrier-Frequency Domain Equalization (SCFDE) systems. Space-frequency (SF)-LDCs are more suitable than space-time (ST) LDC in high mobility environments. However, the application of LDCs in space and frequency domains in SCFDE systems is not straightforward as in orthogonal frequency division multiplexing (OFDM) systems because in this case there is no direct access to subcarriers at the transmitter. This letter shows that it is possible to induce a target SF symbol dispersion in SCFDE by using a simple linear pre-coder and a conventional LDC that spreads the symbols in time and space domains according to specific ST dispersion matrices. The letter shows how to derive the ST dispersion matrices to be used at the transmitter as a function of the dispersion matrices describing the target SF dispersion. The presented procedure can be applied to both pure transmit diversity and pure multiplexing schemes, which are special cases of LDCs. Therefore, the proposed scheme provides a low complexity implementation of any dispersion in space and frequency over SCFDE systems, which alternatively would require the use of FFT/IFFT also at the transmitter side. The letter also shows a performance comparison of SF-LDCs and ST-LDCs in a typical propagation environment for future radio systems. The comparison confirms the suitability of using the dispersion in frequency rather than time for a wide range of coherence bandwidths.

This letter proposes a space-frequency block-coded (SFBC) single-carrier frequency-domain equalization (SC-FDE) system. The transmit sequence of the proposed system is designed to have spatial and frequency diversities, and the corresponding combining receiver is derived under a minimum mean square error criterion. It is shown that the proposed system significantly outperforms the space-time block-coded SC-FDE system over fast-fading channels while providing lower computational complexity than orthogonal frequency division multiplexing combined with the SFBC.

Two transmitter diversity techniques for turbo coded orthogonal frequency division multiplexing (OFDM) are presented: space-time block coding (STBC) and space-frequency block coding (SFBC). With different channel environment and block size, STBC and SFBC have different performance. Also, with the increase of interleaver size (equal to block size for BPSK), turbo has better performance. So the performance of STBC and SFBC with different transmission environment and block size is simulated and discussed. Some important conclusions about the transmitter diversity for turbo coded OFDM systems are achieved.

Time-selectivity in fast fading channels has been one of big obstacles to attain high efficiency and diversity gain for space-times codes. Orthogonal-frequency-division-multiplexing (OFDM) combined with space-time trellis codes has been introduced to combat effect of frequency-selectivity. Subsequently, space-time block codes, space-frequency codes and concatenation with diverse error-correcting codes were investigated. However, for multiple-input multiple-out (MIMO) OFDM systems, to design high-efficiency robust space-time-frequency codes becomes one of big problems. In this paper, we presented pairwise error probability analysis of space-frequency-time block codes, and then concluded one general design criterion for space-time-frequency block codes by utilizing the frequency-correlation feature of sub-channel in mobile OFDM systems. Then, we investigated performance of space-frequency block codes for MIMO-OFDM systems with 4 transmit antennas. And comparison between space-frequency block codes and space-time block codes is performed with different number of transmit antenna. Link-level simulations on COSSAP® verified analytical results. The results show that SFBC is superior to STBC in fast fading channel. And power-delay profile of fading channel, i.e., channel order and delay spread, must be included into design consideration on space-time-frequency codes.

This paper proposes a new scheme of the rate compatible low-density parity-check (RC-LDPC) coded single carrier-frequency domain equalization (SC-FDE) system where RC-LDPC codes are combined with SC-FDE modulations. To construct a class of different RC-LDPC codes, we take advantage of a base matrix constructed by the progressive edge growth (PEG) algorithm. A special code matrix structure is used and modified to meet requirements of the different code rate. In addition, a pseudorandom sequence instead of traditional cyclic prefix (CP) is proposed to estimate the channel noise variance for LDPC decoding. The simulation results show that the modified RC-LDPC codes have better performance than that of current method and the RC-LDPC coded SC-FDE system obtains better performance compared with uncoded SC-FDE system.

In this paper, we investigate and compare the performance of single- and multi-carrier modulation schemes for indoor visible light communication (VLC). Particularly, the performances of single carrier frequency domain equalization (SCFDE), orthogonal frequency division multiplexing (OFDM) and on-off keying (OOK) with minimum mean square error equalization (MMSE) are analyzed in order to mitigate the effect of multipath distortion of the indoor optical channel where nonlinearity distortion of light emitting diode (LED) transfer function is taken into account. Our results indicate that SCFDE system, in contrast to OFDM system, does not suffer from high peak to average power ratio (PAPR) and can outperform OFDM and OOK systems. We further investigate the impact of LED bias point on the performance of OFDM systems and show that biasing LED with the optimum value can significantly enhance the performance of the system. Bit-interleaved coded modulation (BICM) is also considered for OFDM and SCFDE systems to further compensate signal degradation due to inter-symbol interference (ISI) and LED nonlinearity.

In OFDM communication system suitable for the highspeed broadband transmission, ICI (intersubcarrier-interference) caused by phase noise and frequency offset results in poor system performance. In this paper, new STFBC (space time frequency block coding) method combining ICI self-cancellation scheme and antenna, time, frequency diversity is studied to reduce ICI effectively. CPE (common phase error) and ICI are analyzed by the phase noise linear approximation method in the 4 kinds of systems. CIR (carrier-to-interference ratio), PAPR (peak to average power ratio), PICR (peak interference to carrier ratio), BER (bit error rate) and bandwidth efficiency are discussed to analyze the system performance degraded by phase noise of the PLL (or frequency offset) in the 5 kinds of systems. The SCI (self-channel interference) that usually happens in the STBC (space-time block coding) method can be easily avoided in above STFBC method. STFBC method considerably reduces ICI and SCI. Conclusively the proposed STFBC method using diversity technique can show excellent performance without the loss of bandwidth efficiency, compared with the other conventional methods, although it lowers the transmission speed.

This work explores the performances of Space-Time and Space Frequency Coded Orthogonal Frequency Division Multiplexing (OFDM) with simple two branches transmit diversity scheme. The combination of multiple-antenna and orthogonal frequency division multiplexing (OFDM) provides reliable communications over frequency selective fading channels. We focus on the application of space-time block codes (STBC) and space-frequency block codes (SFBC) in OFDM systems over time-varying and frequency-selective channels. SFBC transmitter shows superior performance in fast varying channels while STBC shows better performance in frequency selective channels. A switching technique is presented that selects an appropriate transmission scheme between the STBC and SFBC assuming Rayleigh fading model.

Multiuser multiple-input multiple-output (MU-MIMO) wireless systems that employ single-carrier frequency-domain equalization (SC-FDE) for uplink transmissions can provide high data rates with increased spectral efficiency under severe channel conditions. However, the availability of accurate channel estimates at the base station (BS) receiver is crucial for achieving peak performance. In this paper, we investigate the use of subspace decomposition and derive a novel algorithm for the blind estimation of MU-MIMO channels in SC-FDE systems, as specified by the 3GPP LTE. By exploiting the long data blocks available in LTE standards, our proposed blind algorithm can obtain accurate estimates of the MU-MIMO channels over every block of transmitted data. This provides for a bandwidth-efficient solution in SC-FDE systems by eliminating (reducing) the need to allocate an entire block of pilot sequences for each active transmitter. Furthermore, since the channel estimation is deployed at the BS, the computational complexity is not considered to be a significant burden for future systems in exchange for the increased spectral efficiency. The results of simulations over fading channels, using realistic system parameters representative of LTE-Advanced, demonstrate the advantages of our proposed blind subspace-based channel estimation algorithm and support the feasibility of the resulting MU-MIMO SC-FDE scheme with reduced training.

Single carrier-frequency division multiple access (SC-FDMA) has been adopted as the uplink transmission standard in fourth generation cellular network to enable the power efficiency transmission in mobile station. Since multiuser multiple-input multiple-output (MU-MIMO) is a promising technology to fully exploit the channel capacity in mobile radio network, this paper investigates the uplink transmission of SC-FDMA systems with orthogonal space frequency block codes (SFBC). Two linear multiuser MIMO (MV-MIMO) receivers, orthogonal SFBC (OSFBC) and minimum mean square error (MMSE), are derived for the scenarios with limited number of users or adequate receive antennas at base station.

A combined minimum mean square error (MMSE) and maximum likelihood (ML) multiuser detector with reduced-complexity is proposed for uplink space-time block coded (STBC) orthogonal frequency division multiplexing (OFDM) systems. In this combined detector, received signals from co-channels are first detected by an MMSE multiuser detector. Then an ML-based post-detection processor (PDP) is designed to detect estimated outputs from the MMSE detector with the highest probability of errors and correct them to reduce the system bit error rate (BER). An efficient algorithm is proposed for the PDP which requires only a small additional complexity but can improve the system BER performance significantly compared with the conventional MMSE multiuser detector.

We have been conducting research on a transmission system using ultra-multilevel orthogonal frequency division multiplexing (OFDM) technology and dual-polarized multiple-input multiple-output (MIMO) technology based on the digital terrestrial broadcasting signal format, ISDB-T. As a technology of a single frequency network (SFN) for the next-generation of digital broadcasting, we studied a space time coding (STC) - space division multiplexing (SDM) transmission in which STC and dual-polarized MIMO-OFDM are used together. In this paper, we studied a scattered pilot (SP) scheme for the channel estimation in STC-SDM transmission and the coding schemes. Computer simulations confirmed the advantages of STC-SDM transmission compared with the conventional SFN scheme in environments in which the desired to undesired signal ratio (D/U) is low. We also show the results that STC-SDM transmission with space time block coding (STBC) and space frequency block coding (SFBC) has the same characteristics as transmissions under fixed reception conditions.

In this paper, we first analyze the differences of underwater acoustic (UWA) orthogonal frequency division multiplexing (OFDM) systems and conventional terrestrial OFDM system, and give a simple introduction of the backgrounds. By considering the real UWA channel environments, the measured channel data is used to generate the UWA channel model and calculate the relative parameters for underwater OFDM systems. Practical least square (LS) based channel estimation with linear interpolation are adopted to obtain the channel state information (CSI) at receiver side. As multi-input multi-output (MIMO) processing techniques, Alamouti code is implemented and evaluated to perform for space time block coding (STBC) and space frequency block coding (SFBC) for UWA OFDM systems with the MIMO configuration of , at the same time, maximum ratio combining (MRC) is performed for the purpose of comparison. The simulation results show that, with perfect channel estimation, SFBC failed to work duo to the serious frequency selectivity of UWA channel environments. When the practical channel estimation is applied, in the case of STBC, the proposed 4-column pilot pattern gives better performance about 7dB than SISO system.

For digital terrestrial television broadcasting (DT-TB) systems, orthogonal frequency division multiplexing (OFDM) technique is considered to be an effective method to combat the frequency selective channel cause by multi-path effect. In the single frequency network (SFN) scenario, Alamouti space frequency block coding (SFBC) is introduced to provide spatial diversity gain and improve the link stability. However, both OFDM and Alamouti SFBC are sensitive to time-variant during mobile reception. In this paper, we propose a decision feedback equalization algorithm for inter-carrier interference (ICI) can-celation of the dual (PN) padded time domain synchronization OFDM (TDS-OFDM) DTTB system over doubly selective channel. Our algorithm is proven by numerical simulations which show bit error rate (BER) gain over mobile SFN channel and can be adopted in mobile high density television (HDTV) transmission systems.

In this letter, we address the problem of estimating the integer part of carrier frequency offset (CFO) in space frequency block codes (SFBCs) systems with orthogonal frequency division multiplexing (OFDM) modulation schemes. We derive a maximum-likelihood (ML) estimator assuming that the receiver has two receive antenna, and then we extend the analytical analysis to an arbitrary number of receive antennas. The proposed estimator is designed in a way that exploits the additional two-dimensional space-frequency redundancy provided by SFBCs. Because of its popularity, Alamouti code is chosen to be the code of interest. However, a similar analytical treatment could be applied to any other code. The computational complexity analysis and Monte Carlo experiments are carried out to verify effectiveness of the proposed estimator for practical applications.