Multi-user Transmitter Pre-processing Research Articles

Mitigating Co-channel interference using transmitter pre-processing for double space-time transmit diversity aided IDMA system

A double space-time transmit-diversity (DSTTD) architecture achieves higher throughput by employing four transmit antennas and four receive antennas. In this article, we compute Error-Rate (ER) performance of DSTTD-Interleave-division multiple-access (IDMA) system using Multi-user transmitter pre-processing (MUTP) for standard channel models. We realize MUTP using SVD technique to mitigate Co-channel interference (CCI) effects apart from Multi-user Interference (MUI), which are considered to be major channel impairments. The MUTP exploits the signal space of the entire active user's channel state information (CSI). We estimate CSI and quantize using vector quantization at each mobile unit and formulate TP by recovering at base station. Our simulation result reveals that considered system with MUTP technique achieves better ER with less SNR while offering high data rate for downlink transmission. Further, we observe that the ER performance of our considered system depends on code book size of vector quantized parameters.

Performance of Spread Spectrum Based Multi-Carrier System in Underwater Communication Using Transmitter Pre-Processing

In this paper, we evaluate the bit-error-rate (BER) performance of a turbo-coded, transmitter pre-processing-assisted spread spectrum technology-based multi-carrier (MC) system for the acoustic information transmission in underwater communication. Our primary goal is to improve the power efficiency of the system in terms of signal-to-noise ratio (SNR) while obtaining achievable BER in underwater communication. In underwater communication, inter-symbol-interference and acoustic interference are the two most important issues, which affect the system performance. We use spread spectrum technique to mitigate the effects of unwanted information in the presence of ambient noise. Multi-user transmitter pre-processing (MUTP) is the digital processing method, which is carried out at the transmitter side to offer the low complexity of the receiver. We formulate the singular value decomposition-based pre-processing matrix using noisy feedback of vector quantized (VQ) estimated channel information (CI). We consider the MC communication to mitigate the effects of multi-path propagations. We realize iterative style of decoding algorithm at the receiver to retrieve the acoustic information from the ambient noise contaminated acoustic signals. In particular, we evaluate the error-rate analysis of MC system for realistic channel model based on shallow water channel model, which consists of 11 tap delay. Simulation results emanating from this paper bring to surface the considered coded MC system with MUTP offering a better BER performance with power efficiency regarding SNR while retaining the low complexity of the receiver. Furthermore, we observe that there is an improvement in the system performance when perfect CI is utilized to frame the pre-processing matrix compared with noise contaminated VQ-CI.

Performance of a turbo-coded downlink IDMA system using transmitter pre-processing

In this study, we investigate the bit error rate (BER) performance of a multi-user transmitter pre-processing (MUTP) aided, turbo-coded interleave division multiple access (IDMA) scheme over correlated frequency-selective channels for downlink (DL) communication. We realize MUTP using a zero forcing (ZF) approach. Further, we build the pre-processing matrix using the channel state information of all of the active users. To be specific, we evaluate the BER performance of a coded ZF-MUTP assisted IDMA system for a realistic channel model based on Stanford University Interim channel and Long term Evolution channel specifications; the MUTP is based on both an equal power approach and a maximum-signal-to-noise ratio (MSNR) approach. From our simulation results, we observe that our considered system with a MSNR power allocation regime provides better performance in terms of the achievable BER than the equal power approach, while offering a low complexity receiver for DL transmission.

Performance of feedback multiple‐input–multiple‐output system aided by polarisation multiplexing and pre‐processing

In this study, the authors investigate the performance of a multi-user downlink (DL) multiple-input–multiple-output (MIMO) system aided by polarisation multiplexing (PM) and multi-user transmitter pre-processing (MUTP). Dual- and triply-polarised antennas that are called on to establish PM offer the advantage of replacing uni-polarised antennas that impose space constraints. In a multi-user scenario, users conflict multi-user interference (MUI). In this contribution, the DL-MUI is suppressed with the aid of pre-processing operated at the base station. To be specific, two pre-processing approaches are considered in their study which are based on singular value decomposition. Both the approaches exploit the channel impulse responses (CIRs) of all the users to formulate the pre-processing matrix and that the second approach which is a joint multi-user transmission and detection technique exploits only user specific CIRs to formulate the post-processing matrix. In their contribution, the required CIRs for formulating the pre-processing matrix are acquired via noisy feedback channels that endure fading as well as delay. Simulation results demonstrate that noise and fading tainted CIRs based MUTP results in performance degradation in terms of the attainable symbol-error-rate (SER) and sum-capacity. Moreover, it is inferred that further degradation results when the feedback channels experience delay. However, their study shows that the application of dual or triply-polarised antennas in conjunction with MUTP can serve as an efficient approach for the DL of the feedback MIMO system, as the achievable sum-capacity and SER under ideal feedback remain close to that attained with the perfect CIRs hypothesis. Furthermore, it is observed that the considered MUTP techniques result in superior SER performance compared with their multi-user detection counterpart and other widely known pre-processing techniques.

Performance of Multi-User Transmitter Pre-Processing Assisted Multi-Cell IDMA System for Downlink Transmission

In this paper, we present the performance of multi-user transmitter pre-processing (MUTP) assisted coded-interleave division multiple access (IDMA) system over correlated frequency-selective channels for downlink communication. We realize MUTP using singular value decomposition (SVD) technique, which exploits the channel state information (CSI) of all the active users that is acquired via feedback channels. We consider the MUTP technique to alleviate the effects of co-channel interference (CCI) and multiple access interference (MAI). To be specific, we estimate the CSI using least square error (LSE) algorithm at each of the mobile stations (MSs) and perform vector quantization using Lloyd's algorithm, and feedback the bits that represents the quantized magnitudes and phases to the base station (BS) through the dedicated low rate noisy channel. Finally we recover the quantized bits at the BS to formulate the pre-processing matrix. The performance of MUTP aided IDMA systems are evaluated for five types of delay spread distributions pertaining to long-term evolution (LTE) and Stanford University Interim (SUI) channel models. We also compare the performance of MUTP with minimum mean square error (MMSE) detector for the coded IDMA system. The considered TP scheme alleviates the effects of CCI with less complex signal detection at the MSs when compared to MMSE detector. Further, our simulation results reveal that SVD-based MUTP assisted coded IDMA system outperforms the MMSE detector in terms of achievable bit error rate (BER) with low signal-to-noise ratio (SNR) requirement by mitigating the effects of CCI and MAI.

Performance of relay-aided downlink DS-CDMA system using transmitter preprocessing based on feedback information

In this contribution, we investigate the performance of relay-aided downlink (DL) direct sequence code division multiple access (DS-CDMA) system with multi-user transmitter preprocessing (MUTP) based on vector quantized channel impulse responses (VQ-CIRs). Specifically, the CIRs are estimated with the aid of training-sequence based estimation technique at each of the relays. These estimated CIRs are then VQ and the magnitudes and phases are fed back to the base station (BS) through feedback channels, that conflict noise and fading. At the BS, the CIRs recovered using a linear detector are then exploited to formulate the preprocessing matrix to mitigate the DL multi-user interference at the relays. Our study shows that the attainable bit-error-rate (BER) degrades when noise and fading contaminated VQ-CIRs are invoked to realize the preprocessing matrix. Nevertheless, the resultant BER performance of the MUTP based on VQ-CIRs acquired via ideal feedback remains close to that achieved with perfect CIRs assumption.

Cooperative communication‐aided multi‐carrier code division multiple access downlink transmission with transmitter preprocessing: performance results

In this correspondence, the authors study the performance of multi-user transmitter preprocessing (MUTP)-assisted cooperative downlink (DL) transmission for multi-carrier code division multiple access (MC-CDMA) system, where multi-user interference (MUI) and inter-relay interference (IRI) are the principal channel impairments. Relaying is facilitated with the aid of fixed infrastructure-based relays that perform additional signal processing like formulating the preprocessing matrix for mitigating MUI in addition to forwarding the information they receive from the base station (BS). Specifically, in this study, the authors analyse the performance of cooperative communication-aided DL MC-CDMA system by employing three cooperation strategies: (i) all users supported by a single relay with dominant MUI at the relay and mobile stations (MSs); (ii) each user supported by a single relay where, MUI and IRI are dominant at the relays and MSs, respectively, as well as weak IRI at the MSs; and (iii) all users supported by L relays where MUI is dominant at the relays, and MUI and IRI are dominant at the MSs. Our simulation study shows that MUTP-aided cooperative DL transmission results in better achievable bit error rate than the multi-user detection-aided system as the MUI at the relays and MUI and IRI at the MSs are perfectly eliminated.

Multi-user transmitter preprocessing assisted uplink multi-cell multiple-input multiple-output system with base station cooperation over frequency-selective channels

The performance of cellular uplink multiple-input multiple-output systems, where co-channel interference (CCI) at the base stations (BSs) is a major performance impairment, is investigated in this correspondence principally from a multi-user transmitter preprocessing (MUTP) perspective over correlated frequency-selective channels. Transmitter preprocessing at the mobile station is formulated by singular value decomposition (SVD) of only the individual user’s channel state information (CSI) while post-processing exploits all the users’ CSI using BS cooperation. Our simulations show that this approach completely removes CCI and also outperforms classical zero-forcing multi-user detection, which has about the same detection complexity. Further, the results show that our system, coupled with the optimal ‘water-filling’ strategy for power allocation, results in higher capacity than the maximum signal-to-noise ratio strategy. Furthermore, SVD-based MUTP outperforms dirty paper coding and Tomlinson–Harashima precoding in terms of achievable symbol error rate.

Performance of transmitter preprocessing aided cooperative relaying with fixed infrastructure relays

In this correspondence, we study the performance of cooperative communications with the aid of multi-user transmitter preprocessing (MUTP), both at the base station (BS) and multi-antenna enabled fixed infrastructure based decode and forward relay stations (RSs), for uplink (UL) and downlink (DL) transmissions where, multi-user interference (MUI) and inter-relay interference (IRI) are the domineering channel impairments. MUTP formulated under instantaneous, statistical and imperfect channel state information assumptions at the RSs and BS for UL and DL respectively is based on singular value decomposition and, further at the RSs for DL is based on minimum mean square error principle. Specifically, we investigate the performance of the considered system in the context of weak and dominant MUI at the RSs in UL and dominant IRI at the mobile stations in DL. Our simulation studies show that MUTP aided system achieves better bit error rate than multiuser detection based system.

Performance of multi-user transmitter preprocessing assisted MIMO system over correlated frequency-selective channels

In this contribution we present the performance of a multi-user transmitter preprocessing (MUTP) assisted multiple-input multiple-output (MIMO) space division multiple access (SDMA) system, aided by double space time transmit diversity (DSTTD) and space time block code (STBC) processing for downlink (DL) and uplink (UL) transmissions respectively. The MUTP is invoked by singular value decomposition (SVD) which exploits the channel state information (CSI) of all the users at the base station (BS) and only an individual user’s CSI at the mobile station (MS). Specifically, in this contribution, we investigate the performance of multi-user MIMO cellular systems in frequency-selective channels from a transmitter signal processing perspective, where multiple access interference (MAI) is the dominant channel impairment. In particular, the effects of three types of delay spread distributions on MUTP assisted MIMO SDMA systems pertaining to the Long Term Evolution (LTE) channel model are analyzed. The simulation results demonstrate that MUTP can perfectly eliminate MAI in addition to obviating the need for complex multi-user detectors (MUDs) both at the BS and MS. Further, SVD-based MUTP results in better achievable symbol error rate (SER) compared to popularly known precoding schemes such as block diagonalization (BD), dirty paper coding (DPC), Tomlinson–Harashima precoding (THP) and geometric mean decomposition (GMD). Furthermore, when turbo coding is invoked, coded SVD aided MUTP results in better achievable SER than an uncoded system.

Performance of MUTP-aided MIMO systems over correlated frequency-selective wireless communication channels: a multi-cell perspective

In this article, we investigate the performance of multiuser transmitter preprocessing (MUTP)-aided multiple-input multiple-output (MIMO) systems in a multi-cell multiuser setting where co-channel interference (CCI) is the major channel impairment, for both uplink (UL) and downlink (DL) transmissions. CCI can considerably reduce data rates resulting in outages in cellular systems, particularly at the cell edges in DL transmission. The MUTP considered in this article is based on singular value decomposition (SVD), which exploits the channel state information (CSI) of all the users at the base stations (BSs) with the aid of BS cooperation, and only the individual users' CSI at the mobile stations (MSs) for both UL and DL transmissions. In particular, in this article, we study the effects of three types of delay spread distributions coupled with different interferer configurations over correlated and uncorrelated frequency-selective channels. Our simulation study shows that SVD-aided MUTP perfectly eliminates CCI with lesser detection complexity under perfect CSI. Also, we provide performance comparisons of SVD-aided MUTP with various precoding techniques widely addressed in literature, and the results show that it provides better achievable symbol error rate (SER) by mitigating multi-stream interference (MSI) and CCI. Further, simulation results demonstrate that compared to equal CCI, the presence of a dominant interferer can lead to more degradation in the system performance in terms of achievable SER while, further degradation results when noise is dominant. Furthermore, this study confirms that imperfect CSI as well as imperfect power control can lead to degradation in the system performance.

A zero-forcing multiuser transmitter preprocessing scheme for downlink communications

In this letter a multiuser transmitter preprocessing (MUTP) approach is proposed for downlink wireless communications, such as in spatial-division multiple-access (SDMA) or direct-sequence code-division multiple-access (DS-CDMA) system. In the proposed MUTP the preprocessing matrix is obtained by constructing a subspace that is orthogonal to the interference subspace without relying on eigen-analysis. The proposed MUTP fully removes the downlink multiuser interference, resulting in the zero-forcing (ZF) solution. It is capable of achieving the same bit error rate (BER) performance as the conventional ZF-based MUTP (ZF-MUTP).