In this paper, two turbo interferencecancellation receivers are discussed and are divided into the MMSE front-end turbo space-time partitioned approach receiver (PA) and the MMSE front-end turbo space-timeiterative approach receiver (IA). Numerical results reveal that for an equal number of receiver iterations both IA and PA receivers achieve approximately the same performance for a lightly loaded system at any given performance threshold. However as the system load increases, the IA starts to gain sizable per- formance and capacity gains over the PA receiver. Important to note is that the PA receiver (as compared to the IA receiver) is seen to attain no further performance or capacity gains with an increased number of iterations for the case of a highly loaded system. This poor PA performance can possibly be attributed to the poor parity data decoding performance characteristic of turbo codes.
the FLC system to assign an exact value of μ or λ for the cor- responding adaptive receiver on an iterative basis in order to improve the convergence characteristic and steady-state MSE simultaneously. Most of the fuzzy inference rules are derived by a human expert or extracted from numerical data. In this paper, we focus attention on the fuzzy rules which ac- cumulate past experience operating in the practical applica- tions. Therefore, it seems natural and reasonable to expect that wireless communication systems with the use of a two- parameter ( e 2 , Δe 2 )-FLC produce better convergence char-
associated with 3 , 4 and 5 MSs is similar. When considering the precoded MAP PIC detector using the precoder polynomial of (1 + z −1 ) it can be seen from Figure 6 that especially for K = 3 and 4 MSs the precoding significantly improves the performance compared to the non-precoded system. For K = 5 this performance advantage becomes less pronounced. The BER versus E b /N 0 performance of a 4QAM system is illustrated in Figure 7. The system was characterized by K = 1 , 2 and 3 MSs, each using N Tx = 2 transmit AEs and a BS employing N Rx = 4 receive AEs. The feed-forward order of the joint MMSE STE was chosen to be M = 3 and the channel was assumed to be an equal-power three-tap channel while the interleaver had a length of 64 000 bits. The RSC code considered was again characterized by the octal generator polynomial of [6 5], while the precoded PIC aided MAP STE employed a precoder polynomial of (1 + z −2 ). Similarly to Figure 6, it can be seen from Figure 7 that the advantage of the precoded PIC based STE over the joint MMSE iterative STE is larger for a lower number of transmitters, but it remains
Abstract —In this paper, we propose two simple signal detectors that are based on successive interferencecancellation (SIC) for time-reversal space-time block codes to combat intersymbol interference in frequency- selective fading environments. The main idea is to treat undetected symbols and noise together as Gaussian noise with matching mean and variance and use the already-detected symbols to help current signal recovery. The first scheme is a simple SIC signal detector whose ordering is based on the channel powers. The second proposed SIC scheme, which is denoted parallel arbitrated SIC (PA-SIC), is a structure that concatenates in paral- lel a certain number of SIC detectors with different ordering sequences and then combines the soft output of each individual SIC to achieve performance gains. For the proposed PA-SIC, we describe the optimal or- dering algorithm as a combinatorial problem and present a low-complexity ordering technique for signal decoding. Simulations show that the new schemes can provide a performance that is very close to maximum- likelihood sequence estimation (MLSE) decoding under time-invariant conditions. Results for frequency-selective and doubly selective fading channels show that the proposed schemes significantly outperform the conventional minimum mean square error-(MMSE) like receiver and that the new PA-SIC performs much better than the proposed conventional SIC and is not far in performance from the MLSE. The computational complexity of the SIC algorithms is only linear with the number of transmit antennas and transmission rates, which is very close to the MMSE and much lower than the MLSE. The PA-SIC also has a complexity that is linear with the number of SIC components that are in parallel, and the optimum tradeoff between performance and complexity can be easily determined according to the number of SIC detectors.
be able to track channel variations simultaneously with data transmission. This problem is still not solved in this paper. However, when the symbol timing of the desired signal and the self-interference signal are synchronized, the problem does not arise because specific training symbols are unnecessary. Although this problem is very important, we treat it as a future work in this paper. The rest of this paper is organized as follows. In Section II, a detailed model of the self interference which includes nonlinearities of the IQ mixers and the power amplifier is provided. The proposed selection technique with the frequency domain Hammerstein self-interference canceller is presented in Section III. In Section IV, the performance of the proposed technique under different scenarios is analyzed with equivalent baseband signal simulations
It is interesting to see from Theorem 2 and Corollary 1 that the effective DD domain SNR of the proposed algorithm can theoretically approach the maximum receiver SNR for a given fading channel , with a sufficient number of iterations. Equivalently, this observation indicates that the proposed algorithm can approach the error performance of MLSE theoretically given a sufficient number of iterations. It should be noted that the MLSE can provide the optimal ML error performance, but usually requires a prohibitively high complexity . Therefore, the proposed algorithm can be viewed as a type of reduced-complexity detection algorithm that can potentially approach the optimal error performance. On the other hand, we note that the above analysis is based on Assumption 2. For the case where different resolvable paths share the same delay index, we will demonstrate that the effective DD domain SNR also follows Corollary 1 by numerical simulations. Fig. 5 shows the effective DD domain SNRs with respect to number of iterations. Without loss of generality, the time domain effective channel H eff T is generated according to (13), where P = 4 and the channel coefficients are [ − 0.04 − 0.31i, 0.40 − 0.11i, − 0.43 + 0.18i, 0.59 + 0.21i], the delay indices are [0, 5, 2, 8], and the Doppler indices are [ − 3.08, 3.45, − 3.94, − 0.72], respectively. Similarly, we consider both QPSK and 16-QAM constellations with E s /N 0 = 14 dB and E s /N 0 = 17
Abstract—This paper proposes a fast Minimum-Variance-Distortionless-Response (MVDR) beam- forming algorithm for an antenna array for cancellation of multiple interference signals. The proposed algorithm uses Sample-Average Estimate (SAE) of the data covariance matrix and reduces its compu- tational eﬀort by applying the Matrix-Inversion-Lemma (MIL) to its covariance Matrix Inversion (MI) operation. The proposed algorithm is compared to two SAE-based algorithms: the Sample Matrix Inversion (SMI) algorithm that requires an MI operation and the Auxiliary Vector (AV) algorithm that does not need an MI operation. A non-SAE based algorithm using the Least Mean Square (LMS) method is also included for comparison. Simulation results show that the proposed algorithm converges slower than the SMI scheme but outperforms the AV and LMS schemes during the transient phase. Once convergence is achieved, the proposed algorithm converges to a better Mean Square Error than the rest of the algorithms evaluated.
Lately, interferencecancellation is a hard challenge in a cellular communication system. In this paper, we consider the interferencecancellation using logic OR gate from the multiple input multiple output (MIMO) interference channel where each transmitter and receiver equipped with single or multiple antennas. In our system, we have used a threshold logic unit which is operated by logic OR with NOT operation in the MIMO receiver for interferencecancellation. The threshold unit has two logic threshold signals which are separated by two vectors. These two logic thresholds are denoted by High and Low signal in the threshold unit. The High and Low signals are represented by the desired and interference signal, respectively. Our approach is to practically achieve interference alignment and absolutely cancel to the interference from the received signal by using logic OR operation in the MIMO receiver.
ML decoder is an optimum decoder for MIMO systems but it has an exponential complexity making it difficult to implement for higher order systems. An alternative decoder that obtains near ML performance with reduced complexity is a Sphere Decoder (SD). While the SDA approach provides the ML solution, the run time (operations required) is highly dependent on the received signal-to-noise ratio (SNR), which results in variable throughput as reported in several implementations of the sphere decoder. These approaches can be effectively expressed as tree-searching class of algorithms while only visiting a subset of the tree . The SDAs for MIMO system have two types of searching strategies: the Fincke- Phost (FP) method and the Schnorr-Euchner (SE) strategy. The second method has less computational complexity by re-ordering the constellation searching at each layer .
The design of future broadband wireless systems presents a big challenge, since these systems should be able to cope with severely time-dispersive channels and are expected to have high spectral and power efficiencies. The wireless communication industry has been very successful in recent years in providing high- speed data links that allow a multitude of multimedia applications. Among others, these successes include the terrestrial digital television standard DVB-T. The next generation mobile communication systems are required to support much higher variable data rate services with high quality. In direct sequence code division multiple access (DS-CDMA) mobile communication systems with time-varying multipath channels and additive white Gaussian noise (AWGN), both inter-symbol interference (ISI) and multiple access interference (MAI) must be considered  .
The demand of high data rate and affirmation to the real-time communications (network). LTE is well placed to fulfill the demands of next generation mobile networks. It delivers beneficial features such as high mobility transmission and scalability of bandwidth using both TDD and FDD duplexing methods, for the time varying and frequency selective wireless channel within one OFDM sub-carrier. For the exact estimation of wireless channel, some of OFDM subcarrier used as a reference signal while other subcarrier are either used to transmit data symbols are set as unused. The weighted time-domain interpolation computed from the channel based on the Doppler spread information and Parallel InterferenceCancellation scheme jointly with Decision Statistical Combining (PIC-DSC) technique is used to reduce the ICI and to improve the data symbol detection. Here the adaptive modulation technique is used additionally to adopt the channel condition that maximizes the spectral efficiency and to meet higher throughput instead of retransmission, the transition rate can be cut down, when the channel condition is miserable. So the Quality of Service (QOS) in the time varying wireless channel is maintained.
Multiple-Input Multiple-Output (MIMO) schemes are capa- ble of counteracting the fundamental limitations of wireless transmissions imposed by time-varying multipath fading . More explicitly, recent information theoretic studies [2, 3] have revealed that a MIMO system has a higher capacity than a single-input single-output (SISO) system. In , Wolniansky et al. proposed the popular multi-layer MIMO structure, known as the Vertical Bell Labs Layered Space-Time (V- BLAST) scheme. The V-BLAST receiver is capable of provid- ing a tremendous increase of a specific user’s effective bit-rate without the need for any increase in the transmitted power or the system’s bandwidth. However, its impediment is that it was not designed for exploiting transmit diversity and the decision errors of a particular antenna’s detector propagate to other bits of the multi-antenna symbol, when erroneously cancelling the effects of the sliced bits from the composite signal.
case, in addition to the aforementioned simulation para- meters, we set the carrier frequency to 3.5 GHz and the speed of different users to, 80, 120, 90, and 100 km/h, respectively. The main difference between the two cases is that the system matrix in a Rayleigh fading channel is time variant and severely ill-conditioned due to the na- ture of the time-varying fading channel. This imposes some challenges to the performance of the Morozov- LPIC detector where due to the time varying nature of the condition number a fixed weighting factor that might be optimal for one ODFM symbol might result in bad performance for another symbol. In order to over- come this problem, a reasonably small value of the weighting factor should be selected to achieve good per- formance at the expense of slow convergence rate.
energy, it will inevitably combine both the multiple access interference (MAI) and the multipath interference (MPI) in case of communicating over a dispersive multipath channel. To circumvent this problem, the family of loosely synchronized (LS) codes ,  has been proposed, which exhibits a so- called interference-free window (IFW). More explicitly, these codes are capable of suppressing both the MAI and MPI, provided that these interfering components arrive within the IFW. Hence, when the dispersive channel’s delay spread does not exceed the width of the IFW, we can combine all the paths’ energy without imposing any MAI and MPI interference, and hence, interference-free CDMA communication becomes possible without the employment of high-complexity multiuser detection. Furthermore, we will demonstrate that even when the channel’s delay spread does exceed the width of the IFW, the proposed LS code-based STS scheme is capable of outperform- ing the conventional STS scheme. However, the disadvantage of the LS code-based STS scheme advocated is that the number of available LS codes is limited when aiming for a specific spreading gain G . More explicitly, the number of supported users and the width of the IFW ι must satisfy K(ι + 1) ≤ G . To expound a little further, we can achieve a high IFW width and suppress the interference more effectively when the number of users supported in the channel is relatively low because the number of codes exhibiting a high IFW is low. By contrast, as the number of users increases, the IFW width tends to zero since all the codes having a wide IFW have been activated, and hence, the LS code-based STS scheme becomes incapable of suppressing the MAI and MPI.
SIC has high potential of sending or receiving multiple signals concurrently, which improves the transmission e ffi ciency. In , the authors developed MAC and routing protocols that exploit SC and SIC to enable simultaneous unicast transmissions. Sen, et al. investigated the possible throughput gains with SIC from a MAC layer perspective . Power control for SIC was comprehensively investigated and widely applied to code division multiple access (CDMA) systems [1, 4, 5, 14, 22]. Applying game theory, Jean and Jabbari proposed an uplink power control under SIC in direct sequence-CDMA networks . In , the authors introduced an iterative two-stage SIC detection scheme for a multicode MIMO system and showed the proposed scheme significantly outperformed the equal power allocation scheme. A scheme on joint power control and receiver optimization of CDMA transceivers was presented in . In [1, 4], the impact of imperfect channel estimation and imperfect interferencecancellation on the capacity of CDMA systems was examined.
namely code division multiple access (CDMA), gives high flexibility, robustness, and frequency diversity gains . Re- cently, the cellular aspects of MC-CDMA were investigated. In [8, 9], first analyses regarding the intercell interference modeling for cellular MC-CDMA environments are given. A Gaussian approximation was proposed for the intercell inter- ference modeling which was verified with more analytical in- vestigations in [10, 11]. This simplified intercell interference assumption allows a large reduction of the simulation com- plexity for cellular MC-CDMA systems. In [12, 13] the main focus was on the overall performance of an MC-CDMA sys- tem in a cellular environment. It was shown that there exist large performance degradations in the cell border area. Even a sectorized cellular system could not reduce these degrada- tions .
Carrier frequency offset, caused by Doppler shift, and time-varying channel bring the intercarrier interference. Several ICI cancellation schemes have been proposed, and ZF (zero forcing) detection scheme is one of them. Although conventional ZF detection scheme is widely used in noise free environment, the noise enhancement occurs while suppressing the ICI effect. Wiener solution has been proved to be able to detect signals without noise enhancement . On the other hand, successive interferencecancellation scheme has been successfully used in MC-CDMA and OFDM systems to mitigate multiple access interference and intercarrier interference respectively [9-10]. In this paper, we first study the performance of Wiener- based SIC for OFDM systems over fading channels. Although the Wiener- based SIC scheme can provide good ICI cancellation performance, its computation complexity increases as number of subcarriers increases . This is a trade-off between bit error rate (BER) performance and computation complexity. Therefore, we further study a modified Wiener-based SIC ICI cancellation scheme to reduce computation complexity without reducing BER performance or with minor BER performance degradation.
Starting with the increasing demands for higher data rates in future networks, different technologies (e.g. multiple-input multiple output (MIMO) and beamforming) are being studied , . Combining MIMO and beamforming offer higher data rates. Beyond the conventional beamforming schemes, data rates at the receiver can be improved through directional and multi-directional beamforming schemes , , a good candidate for millimeter wave (mmWave) MIMO systems in the forthcoming 5G network . Space-time block codes (STBC)  are MIMO design techniques with the potential of increasing received data rate and reducing the bit error ratio (BER) especially when operated with beamforming.
Hyung G. Myung and David J. Goodman  published a book describing SC-FDMA. Book describes the frequency division modulation technique schemes used in wireless systems and its features. A comparison of SC-FDMA system with other techniques like frequency domain equalization, orthogonal frequency division modulation and orthogonal FDMA is also given. The time domain as well as frequency domain operation of SC-FDMA as well as signal processing is given in detail. The details regarding implementing SC-FDMA in 3GPP LTE like implementation standards are also mentioned. Meng Ma  in his letter to IEEE mentioned a new interference self cancellation scheme for SC-FDMA signals. The objective was to reduce the ISI caused by frequency offset and Doppler shift in SC-FDMA signals. They have considered only the localised SC-FDMA signals. The author concluded like the first symbol that we are transmitting will cause a major interference and distortion for adjacent symbols. So to mitigate the interference the solution was to suppress the first symbol and use that free space for transmitting other symbols for synchronization or error correction. . With little bandwidth sacrifice the proposed scheme has improved the system performance to a very high extent. Also the system robustness against frequency offset. K. Raghunath and A. Chockalingam  conducted a detailed comparative study of SC-FDMA and OFDMA signals on sensitivity to CFO and TO is done by the author. He has concluded with the following ideas.