Integer-Forcing Message Recovering in Interference Channels

We present a successive interference cancellation (SIC) scheme for a multicarrier (MC) DS CDMA system. In every subband, the SIC receiver successively detects the interferers' signals and substracts them from the user-of-interest. A comparison is made among SIC, matched filter detection with an equal gain combiner (MF-EGC), matched filter followed by maximal-ratio combining (MF-MRC) and minimum mean-squared error (MMSE) receivers with optimal tap coefficients. For this latter receiver, we determine the performance both when the number of taps equals the processing gain, denoted by N, and when the number of taps is roughly one-half of the processing gain. By analysis and simulation, it is shown that the SIC has better ability to suppress multiple-access interference (MAI) than do MF and [N/2]-tap MMSE in single carrier (SC) CDMA, and MF-EGC, MF-MRC and [N/2]-tap MMSE in MC CDMA, and this translates to increased capacity and better fading resistance. Further, SIC and N-tap MMSE yield approximately the same performance in SC CDMA, but SIC has a poorer performance than does an N-tap MMSE in MC CDMA. In addition, we derive results for the performance degradation that a SIC scheme experiences in MC CDMA due to both phase and timing tracking errors. It is shown that with small tracking errors, SIC can still retain a performance advantage over MF-EGC and MF-MRC, although the advantage of SIC decreases with increasing tracking errors.

We present a successive interference cancellation (SIC) scheme for a multicarrier (MC) direct-sequence code-division multiple-access (CDMA) system, using band-limited spreading waveforms to prevent self-interference. In every subband, the SIC receiver successively detects the interferers' signals and substracts them from the user-of-interest. A comparison is made among SIC, a minimum mean-squared error (MMSE) receiver, and matched filter (MF) detection with maximal-ratio combining (MRC). We also consider suboptimal combining using pilot symbol-assisted modulation (PSAM) to make the system more realistic. Analytic bit-error probabilities for SIC, MMSE, and MF in correlated Rayleigh fading channels are derived. The theoretical results for SIC, MMSE, and MF are shown to agree well with simulations. In particular, SIC and MMSE are shown to achieve better performance than MF with MRC; when the number of users is small, SIC provides better performance than does MMSE. Further, the correlation among different subcarriers is studied, and only large subcarrier correlation coefficients result in an obvious worsening of performance. Finally, we derive results for the performance degradation that an SIC scheme experiences in MC CDMA due to phase and timing tracking errors. It is shown that SIC can still retain a performance advantage over MF-MRC, although the advantage of SIC decreases with increasing tracking errors, especially when subcarrier correlation coefficients are small.

Long Term Evolution - Advanced systems are currently being standardized by 3GPP and aim at very high peak data rates of 1 Gb/s in the downlink and 500 Mb/s in the uplink. Those ambitious targets can only be achieved by using advanced MIMO antenna techniques as well as wide spectrum allocation, up to 100 MHz. A multiple component carrier structure has been agreed on in the 3GPP Work Item as a solution to extend the 18 MHz bandwidth of the previous LTE Release 8 up to 100 MHz. The multiple access schemes on both uplink and downlink now have to be adapted to the new spectrum configuration. Furthermore, in the link adaptation design the transmission over multiple CCs would reasonably lead to an increase of the feedback overhead. Bundling of the spatial or frequency parameters can keep the overhead low at the cost of lower throughput. In this article, we consider as a study case the LTE-A uplink, where NxDFT-spread- OFDM has been selected as the multiple access scheme. The validity of this scheme for the uplink is evaluated in terms of cubic metric, which is an indicator of the power de-rating needed at the transmitter to avoid intermodulation distortion. Furthermore, the impact of bundling the link adaptation parameters on the link performance is discussed considering both linear and turbo successive interference cancellation (SIC) receivers. Two codeword mixing stategies in the frequency and spatial domains are also proposed to boost the performance when the bundling is made per antenna or per CC, respectively. Results show that when a linear receiver is used in the base station, mixing techniques can increase spectral efficiency, thus reducing the performance gap to the no bundling case, which is the most expensive solution in terms of feedback signaling. However, when a turbo SIC receiver is used, only mixing over CCs is a valid option to achieve link performance gain.

In this paper, we deal with the design of high-rate space-time block codes (STBCs) that achieve full-diversity with linear receivers which enable symbol-wise decoding. We propose three new high-rate coordinate interleaved STBCs and prove that they can achieve full-diversity with linear receivers for any optimally rotated square QAM constellation. Recently, Shang and Xia proved that the symbol rate of an STBC achieving full-diversity with a linear receiver is upper bounded by one complex information symbol per channel use (pcu). However, we show that with the use of coordinate interleaving, the proposed STBCs can exceed this upper bound to 4/3 complex information symbols pcu for two, three and four transmit antennas. For the symbol-by-symbol decoding of the proposed STBCs, we adapt the partial interference cancellation (PIC) group decoding algorithm recently proposed by Guo and Xia, and then further modify this decoder by applying successive interference cancellation (SIC) operation. Simulation results show that when linear receivers with minimum decoding complexity are used, the proposed STBCs achieve better error performance than their counterparts given in the literature.

This work proposes a new coding scheme for the discrete memoryless two-user interference channel whose receivers can cooperate to decode their desired messages. The coding scheme is built upon Han-Kobayashi rate splitting and superposition coding at the transmitters, noisy network coding, and non-unique joint decoding at the receivers. As a case study the general achievable region leads to an inner bound for the Gaussian interference channel whose receivers cooperate through rate-limited orthogonal channels. It is shown that this inner bound is equivalent to the one-round quantize-bin-and-forward inner bound established by Wang and Tse, thereby showing that noisy network coding achieves within 1 bit/s/Hz to the capacity region when the interference is strong, and achieves within 1 bit/s/Hz to the capacity region of the Gaussian compound multiple access channel with conferencing decoders regardless of channel parameters.

An investigation has been made on the models and characteristics of triple-frequency carrier-phase linear combinations for the BeiDou Navigation Satellite System (BDS). Based on the three frequencies of the BDS, three categories of combinations are developed: ionosphere-free combinations (i.e., those that eliminate the ionospheric effect), minimum-noise combinations (those that mitigate the effects of thermal noise and multiple paths), and troposphere-free combinations (those that mitigate tropospheric effects). Both the ionosphere-free and troposphere-free combinations can be expressed as planes, whereas the minimum-noise combinations can be expressed as a line. The relationships between these three categories of linear combinations are investigated from the perspective of geometry. The angle between the troposphere-free plane and ionosphere-free plane is small, while the angles between the troposphere-free plane and the minimum-noise line, and between the ionosphere-free plane and the minimum-noise line, are large. Specifically, the troposphere-free plane is orthogonal to the minimum- noise line. By introducing the concepts of lane number and integer ionosphere number, the characteristics of the long-wavelength integer combinations and ionosphere-free integer combinations are investigated. The analysis indicates that the longest wavelength that can be formed for integer combinations is 146.53 m, and the ionosphere-free integer combinations all have large noise amplification factors. The ionosphere-free integer combination with minimum noise amplification factor is (0, 62, 59). According to the lane number, integer ionosphere number, and noise amplification factor, optimal integer combinations with different characteristics are presented. For general short baselines and long baselines, three independent integer combinations are suggested.

SummaryCooperative communication is a significant technology for fifth generation (5G) and beyond wireless communication to improve the quality of service (QoS) in massive networks. In addition, it serves as a promising candidate along with non‐orthogonal multiple access (NOMA) scheme to increase the spectral efficiency. Conventionally, cooperative‐NOMA (C‐NOMA) systems are analysed by assuming perfect successive interference cancellation (SIC) and imperfect SIC (I‐SIC) over Rayleigh, Rican, Hoyt fading channels, and so on. In this paper, near–far relay (NFR) C‐NOMA system is analysed aiding perfect SIC, perfect channel state information (CSI), imperfect (I‐CSI) and (I‐SIC) over Rayleigh fading channel. Initially, we derive analytical expressions of outage probability (OP) by considering I‐SIC and I‐CSI for NFR‐C‐NOMA system. The accuracy of analytical results is verified through Monte Carlo (MC) simulations. Interpretation of the results conveys that I‐CSI and I‐SIC have a substantial impact on OP in NFR‐C‐NOMA scheme and existing schemes. Later, we examined impact on OP in NFR‐C‐NOMA by varying relay position, target rate of users and jointly considering the I‐SIC, I‐CSI. Further, it is also observed that the NFR‐C‐NOMA scheme shows better outage performance than state‐of‐the‐art schemes.

Abstract-- As a promising radio access technology for future 5G network, novel multiple access (NMA) is aimed to improve spectrum efficiency and access capability via design of successive interference cancellation (SIC) amenable pattern in single domain (e.g. power domain, code domain, and space domain) or joint multiple domains. In this paper, a pattern in joint space and power domain is designed for NMA system. The proposed pattern jointly adopts a quasi-orthogonal space-time block code (Q-OSTBC) in space domain and power allocation (PA) scheme for users in power domain, which is in conjunction with SIC based linear receiver. The pattern utilizes Q-OSTBC with unequal diversity order to mitigate the error propagation in the SIC based detector for each user, and PA for multiple users with different channel gain to improve the spectrum efficiency. Simulation results show that the designed pattern can effectively mitigate error propagation in SIC based system. We also investigate the performance of SIC based receiver with or without channel decoding during the reconstruction of interference, simulation results indicate that the reconstruction with decoding outperform the one without decoding, especially under the condition of low signal-to-noise ratio (SNR). Due to the diversity gain, the NMA system using the designed pattern can obtain higher average sum rate compared to its counterpart, i.e. the combination of Vertical Bell Layered Space-Time code (VBLAST) and PA.

The problem of designing linear transmit signaling strategies for the multiple input, multiple output (MIMO) interference channel is considered. For this problem, the best known iterative solution, in terms of maximizing signal to interference plus noise ratio (SINR) at the receivers, is the Max SINR algorithm. However, there is no proof that the Max SINR algorithm converges. In this paper, a modification to the Max SINR algorithm is proposed, in which a power control step is used to make a metric similar to the sum rate increase monotonically with each iteration, thus making the modified Max SINR algorithm convergent. It is further shown that with successive interference cancellation (SIC), the metric that the modified Max SINR algorithm optimizes is exactly the sum rate. Finally, simulations are used to demonstrate that the performance of the modified Max SINR algorithm, unlike other convergent alternatives, is nearly identical to that of the original Max SINR algorithm.

We study the two-user multiple-input single-output (MISO) Gaussian interference channel where the transmitters have perfect channel state information and employ single-stream beamforming. The receivers are capable of performing successive interference cancellation, so when the interfering signal is strong enough, it can be decoded, treating the desired signal as noise, and subtracted from the received signal, before the desired signal is decoded. We propose efficient methods to compute the Pareto-optimal rate points and corresponding beamforming vector pairs, by maximizing the rate of one link given the rate of the other link. We do so by splitting the original problem into four subproblems corresponding to the combinations of the receivers' decoding strategies - either decode the interference or treat it as additive noise. We utilize recently proposed parameterizations of the optimal beamforming vectors to equivalently reformulate each subproblem as a quasi-concave problem, which we solve very efficiently either analytically or via scalar numerical optimization. The computational complexity of the proposed methods is several orders-of-magnitude less than the complexity of the state-of-the-art methods. We use the proposed methods to illustrate the effect of the strength and spatial correlation of the channels on the shape of the rate region.

In this paper, we investigate a downlink non-orthogonal multiple access (NOMA) system consisting of a base station (BS) and two users, where each user decodes its own signal through successive interference cancellation (SIC). When the signal of one user, called the weak user (WU) who has a bad channel, is being decoded, the signal of the other user, called the strong user (SU) who has a good channel, acts as interference. In an interference channel, we can increase the achievable rate by applying improper Gaussian signaling (IGS). Therefore, we apply IGS to SU, aiming to mitigate the interference. We also consider imperfect SIC at SU, which is a more general assumption for a NOMA system. For the considered NOMA system model, we derive the outage probability of each user in a closed form, provide its asymptotic expression, and obtain its diversity order. We also derive the ergodic rate of each of the two users in a closed form. We propose two algorithms to maximize the fairness of the NOMA system based on the primal decomposition method. Through simulation, we verify that our analysis is correct, and confirm that applying IGS improves the fairness of the NOMA system.

Precoding for multiple-input multiple-output (MIMO) spatial multiplexing generally requires high feedback overhead and/or high-complexity processing. Simultaneous reduction in transmitter complexity and feedback overhead is proposed by imposing a diagonal structural constraint to precoding, i.e., power allocation. Minimum bit-error rate (MBER) is employed as the optimization criterion, and an approximate MBER (AMBER) power-allocation algorithm is proposed for a variety of receivers, including zero-forcing (ZF), successive interference cancellation (SIC), and ordered SIC (OSIC). While previously proposed precoding schemes either require ZF equalization for MBER, or use a minimum mean-squared error (MMSE) criterion, we provide a unified MBER solution to power allocation for ZF, SIC, and OSIC receiver structures. Improved error-rate performance is shown both analytically and by simulation. Simulation results also indicate that SIC and OSIC with AMBER power allocation offer superior performance over previously proposed MBER precoding with ZF equalization, as well as over MMSE precoding/decoding. Performance under noisy channels and power feedback is analyzed. A modified AMBER algorithm that mitigates error propagation in interference cancellation is developed. Compared with existing precoding methods, the proposed schemes significantly reduce both transmit processing complexity and feedback overhead, and improve error-rate performance

The multiuser detection is a signal processing tech- nique which enhances the performance and capacity in DS- CDMA technology. Since its complexity issue was too expensive to handle, there was focus on the suboptimal detectors. In this paper we propose a hybrid method called adaptive differential interference cancellation method (ADIC) which is a hybrid of the differential interference cancellation method and which is then combined in a adaptive way to determine a weight matrix which will map the outcome of the differential interference cancellation method to come out with a better performance. This paper also looks into the computational cost of different methods using the floating point operation (flops) which is a good estimation of the comparative computational cost if not the exact one. I. INTRODUCTION The conventional DS-CDMA match filter detector fails to combat these issues due three prominent drawbacks: unrealis- tic ucorrelated code, near-far problem (even with strict power control (1)), and tough multiple access interference (MAI). Many advanced signal processing approaches have been made to improve the performances of these kinds of detectors. In this paper we will study the different approaches that were made in this field and implement these methods to reach a conclusion about the detection methods. As the name of the topic suggests the focus of our work will be study and propose cost effective better performing multiuser detection method. We will explore Multiuser Detection Techniques in Synchronous CDMA environment. Multi-user detection deals with the development and ap- plication of joint demodulation and interference cancellation cancellation techniques for improved detection of a desired set of digital signals in the presence of multiple access interfer- ence, intersymbol interference and noise. Since veterbi forward dynamic algorithm (2) is used in case of Optimum multiuser detection (3) the complexity grows in with the increase in the number of users. Hence the complexity is immense which increases exponentially with the increase in the number of users. Looking ahead for lower complexity hence lesser cost of implementation, the paper proposes the use of sub-optimal linear detectors (4). The sub-optimal detector the paper next focuses on is Decorrelator type of Detector (5) which is optimal in least squares. This detector out performs the optimal detector in many respects. Then the Minimum Mean Square Error (MMSE) linear detector is proposed which tries to minimize the squared error from the required transformation. It is one of the most popular detectors in use due to its easiness to implement and its lower complexity. But then in the above detection methods the decisions made were based on certain linear transformation criterion and there are missing efforts to check the performance in between the detection process to improvise the transformation method better detection. So then the paper proposes Adaptive multiuser detection. Then the paper focuses on Interference cancellation methods which utilize the feedback to reduce Multiple Access Interference (MAI) in the detected bits. Under the Interference Cancellation umbrella the Successive Interference Cancellation (SIC) (6), (7) method is explored and simulated to observe the results. Then the next method which performs better than SIC and more commonly used in real life, called Parallel Interference Cancellation (PIC) (6), (8) is also implemented. Before going ahead to implement the final proposed detection method, this paper implements Differential Interference Cancellation (DIC) (9) method. And then this paper finally proposes an Inter- ference Cancellation method called the Adaptive Differential Interference Cancellation Multiuser Detection method which is cost effective in comparison to other Interference Cancellation methods as we will require lesser hardware (multipliers as in the SIC or Parallel Interference Cancellation (PIC)) for that matter. More ever since we are using adaptive method the desired BER can be further reduced. This proposed method will be discussed in detail in the following section.

Low-complexity lattice reduction algorithms are generally not optimized for solving the shortest basis problem (SBP). We fill this blank by tweaking the recently introduced sequential reduction (SR). In a quest for developing a provable and low-complexity reduction algorithm under the SR framework, we propose to employ successive interference cancellation (SIC) as a subroutine inside SR, and the whole algorithm is referred to as SR-SIC. On the theoretical front, we prove that the upper bound on the basis length of SR-SIC is better than those of major Lenstra, Lenstra, and Lovász (LLL) based variants when the dimension of the lattice basis is no larger than 4. In practice, we show by simulations that SR-SIC yields higher information rate than LLL when designing integer-forcing linear receivers, in which SR-SIC also enjoys lower computational complexity.

Superposition coding (SC) is a nonorthogonal scheme for downlink communications, in which all users are allowed to use the full degrees of freedom of the channel and successive interference cancellation (SIC) is adopted for user decoding. Combining SC with orthogonal frequency-division multiplexing (OFDM) modulation, the optimal resource allocation depends on the perfect channel state information (CSI) of all users at the transmitter, which is hard to obtain for underwater acoustic (UWA) channels. In this paper, we propose a practical OFDM-modulated SC scheme for downlink UWA communications, where the transmitter splits the power between two users based on statistical CSI. The expressions to characterize the boundary of the ergodic rate region achievable by the proposed scheme over long codewords are presented first, followed by the analysis of outage probability when coding is applied within one OFDM block. Then we examine the performance of SC in an OFDM-modulated system with practical coding and modulation pairs. Simulation results show that the OFDM-modulated SC scheme outperforms the orthogonal frequency-division multiple access (OFDMA) in performance of both block error rate (BLER) and spectral efficiencies under different data rate pairs. Recorded data from both medium-range and short-range sea tests verify that channel statistics are stable over a long period of time and can be used to assist resource allocation for the proposed scheme. Compared with OFDMA, considerable increase of spectral efficiencies has been found for SC based on experimental data when both users with disparate channels have nonzero data rates.