An adaptive space-time DFE combined with successive interference cancellation

Space division multiple access (SDMA) has attracted considerable attention as a means for increasing the capacity in cellular communications. For the service provider the smart antenna could provide a much-needed device to boost capacity by decreasing the effect of interference and thereby increase user capacity in congested areas. However, questions arise as to the best trade-offs for implementing SDMA. In this paper, we develop a tool for evaluating the use of SDMA in time division multiple access (TDMA) systems. The approach is based on evaluating the outage probability due to cochannel interference in fading at the base station of a TDMA system assuming an ideal beamformer model. The statistical model developed takes into account both spatial and temporal components of the interference signal. We use the model to then bound the performance improvement. The performance improvement is with respect to a base station employing an omnidirectional antenna. The bounds for the performance are based on looking at a range of smart antenna complexity. In addition, TDMA systems with different levels of acceptable time coincidence between the desired mobile's signal and interfering mobiles' signals are considered. The simulation results indicate a performance improvement spread from 8 to 36 dB.

Ever since the adoption of the single carrier frequency division multiple access (SC-FDMA) scheme for the uplink in the Long Term Evolution (LTE) standard, there has been much interest in improved receiver algorithms for the same. Successive interference cancelation (SIC) based turbo receivers (Turbo SIC) have been proposed to tackle the multi-stream interference (MSI) for transmission modes such as spatial multiplexing (SM) and multiuser (MU) multiple input multiple output (MIMO). In addition, decision feedback equalizers (DFE) have been discussed as an alternative to the simple linear minimum mean square error (LMMSE) based receivers to suppress intersymbol interference (ISI) caused by the frequency selective multi-path channel. This paper proposes a DFE receiver variant based on parallel interference cancelation (PIC) with maximum likelihood detection (MLD) and ordered SIC (OSIC) principles to suppress ISI and MSI. Simulations show that the proposed receiver performs better than the existing SIC and DFE based receivers and achieves the matched filter bound (MFB) for both coded and uncoded systems.

Broadband fixed wireless access (BFWA) systems with multi-hop mesh topologies operating at millimeter-wave bands have attracted considerable attention as a promising technology for high capacity access infrastructures. The primary advantage of the mesh network is an improvement of capacity by means of traffic engineering throughout the network. This work discusses an adaptive load balancing method that enables us to maximize the capacity for the mesh BFWA networks by transferring traffic using multiple routes. Considering wireless link qualities, the adaptive traffic load balancing method attempts to equalize each wireless link's utilization. The proposed method implements flow-based traffic load balancing in order to avoid deteriorating the performance of TCP communications. The performance of the proposed adaptive traffic load balancing method is evaluated on experimental mesh network environments.

Broadband fixed wireless access (BFWA) systems operating above 17-GHz band are suitable for high-density deployment of high capacity wireless access infrastructure, while the radio link quality can suffer from rain attenuation especially in rainy climatic regions. In order to overcome the problem and enhance not only the reliability but also the total capacity of the system, the authors have proposed a multi-hop BFWA system with mesh topology. Its unique characteristics include the modulator/demodulator (MODEM) that can adaptively support QPSK, 16 QAM, 64 QAM, 256 QAM and 1024 QAM operation. It has the maximum transmission capacity of 52 Mbits/s per channel at 6.75 MHz symbol rate and attains 364 Mbits/s by multi-channel configuration over the entire 60-MHz bandwidth at 26-GHz band. This paper presents design and implementation of the MODEM together with various data including bit error curves that demonstrate the validity of the design and implementation. A one-year field experiment commenced in April 2004.

For ultralow-power Internet of Things, we consider a monostatic multiantenna backscatter communication network (MBCN) supporting massive devices through nonorthogonal multiple access (NOMA) over space division multiple access (SDMA). For the network, we optimize the transmit beamforming (BF) for signal excitation of a reader, reflection coefficients of devices for backscattering and energy harvesting, and receive BF for information decoding at the reader toward the maximum fairness in data collection. We first show that the optimization problem for the MBCN without successive interference cancellation (SIC) has a similarity with the problem considered for a wireless power communication network but the conventional algorithm is not applicable to the MBCN with SIC. Thus, we propose a new alternating optimization algorithm that is applicable to both problems with and without SIC at a lower complexity. Simulation results show that the proposed algorithm provides a remarkable gain over the conventional one for the MBCN with SIC while exhibiting a similar performance for the MBCN without SIC. In addition, NOMA/SDMA enhanced by the proposed algorithm increases the minimum system throughput as well as the total energy harvested in the network by utilizing limited resources more effectively for a larger number of devices.

Space division multiple access (SDMA) is a technique that can be superimposed on traditional multiple access schemes such as frequency division multiple access (FDMA), time division multiple access (TDMA) or code division multiple access (CDMA) to increase the system capacity. Several different studies have shown the effectiveness of SDMA in a mobile communication environment. This paper derives a modified formulation for SDMA blocking probability from Galvan-Tejada and Gardiner's (1999) derivation and the cellular traffic theory (Lee and Miller, 1998). A simulation is also presented to verify our derivation.

This paper uses a detailed site-specific channel model to analyze the impact of path loss and co-channel interference (CCI) in a multi-base station broadband fixed wireless access (BFWA) network. The base stations are deployed in an urban setting and make use of sectorised multi-element arrays to suppress CCI from other cells/sectors. Customer premises equipment (CPE) is mounted at rooftop level on a number of surrounding buildings. Spatially correlated multiple input multiple output (MIMO) channels are produced for each link using channel data generated from the ray-tracing model. The tool predicts MIMO correlation based on radiowave propagation and antenna array geometries. The paper considers the use of uniform linear arrays (ULA) and Uniform circular arrays (UCA) with a number of different element spacings. The results provide a unique insight into the deployment of multi-element WiMAX networks in an urban setting.

In this paper, we propose two simple signal detectors that are based on successive interference cancellation (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 parallel 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 ordering 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.

Filter-bank multi-carrier (FBMC) modulations have recently been considered for the emerging wireless communication systems as a means to improve the utilization of the physical resources and the robustness to channel time variations. FBMC divides the overall frequency channel in a set of subchannels of bandwidth proportionally decreasing with the number of subchannels. If the number of subchannels is high enough, the bandwidth of each subchannel is small enough to assume that it is approximately flat. On the other hand, space-division multiple access (SDMA) is a recognized technique to support multiple access in the downlink of a multi-user system. The user signals are precoded at the base station equipped with multiple antennas to separate the users in the spatial domain. The application of SDMA to FBMC is unfortunately difficult when the channel is too frequency selective (or when the number of subchannels to too small) to assume flat subchannels. In that case, the system suffers from inter-symbol and inter-subchannel interference, besides the multi-user interference inherent to SDMA. State-of-the art solutions simply neglect the inter-symbol/subchannel interference. This article proposes a new SDMA precoder for FBMC capable of mitigating the three sources of interference. It is constructed per subchannel in order to keep an acceptable complexity and has the structure of a filter applied on each subchannel and its neighbors at twice the symbol rate. Numerical results demonstrate that the precoder can get rid of all the interference present in the system and benefit therefore from the diversity and power gains achievable with multiple antenna systems.

The two time slots and three time slots amplify-and-forward protocols Time Division Multiple Access (TDMA) based protocols have been investigated previously by various researchers. However, the low diversity order reduces the performance of these TDMA based protocols and has several limitations. Therefore, in this work Enhanced Amplify-and-Forward (EAF) three time slots TDMA based protocol with inter-relay communication has been proposed. Moreover, the normalization factor has been derived, for the 3 rd time slots, to further enhance the performance of the proposed protocol. Due to the improved diversity order and derived normalization factor, the EAF protocol showed low BER and high BER-Gain, as compared to previous proposed AF two time slots and three time slots TDMA based protocols. The proposed protocol is also evaluated by using Global-Percentage-Error-Decrease (GPED) and Local-Percentage-Error (LPED) methods. The proposed protocol showed improvement over previous proposed two time slots protocol, in terms of high GPED in BER of 77.28% at K=1, 46.85% at K=3. From the comparison with PPAF three time slots protocol, the EAF protocol demonstrated GPED in BER of 54.85% at K=1 and 51.26% at K=3. Moreover, the EAF protocol indicated high LPED in BER, as compared to PPAF two time slots and three time slots protocols, with the increase in SNR values.

In this paper, we consider a multiple-access channel, where multiple users equipped with energy harvesting batteries communicate to an access point. To avoid consuming extra energy on competition for the channel, the users are supposed to share the channel via time division multiple access (TDMA). In many existing works, it is commonly assumed that the users' energy harvesting processes and storage status are known to all the users before transmissions. In practice, such knowledge may not be readily available. To avoid excessive overhead for real-time information exchange, we consider the scenario where the users schedule their individual transmissions according to the users' statistical energy harvesting profiles. We first study the optimal transmission scheme in the case where each node has an infinite-capacity battery. By optimization theory, we show that, to maximize the average system throughput, all the users should transmit at an identical optimal power, which solely depends on the energy harvesting rate per time slot. We then study the equal-power TDMA scheme in the case where each node is equipped with a battery of finite capacity. The system is formulated as a polling system consisting of multiple energy queues and one server. By the Markov chain modeling method, we derive the performance of equal-power TDMA in this case, in terms of the energy loss ratio and average system throughput. In addition, we develop an algorithm to efficiently compute the optimal transmission power in the finite-capacity battery case. We also consider an equal-time TDMA scheme, which assigns equal-length subslots to each user, and analyze its system performance. It is found that equal-power TDMA always outperforms equal-time TDMA in the infinite-capacity battery case, whereas equal-time TDMA exhibits compatible or even slightly better performance in some scenarios when the batteries have finite capacities.

Non-orthogonal multiple access (NOMA) has been viewed as a promising technology in future cellular network to increase channel capacity and frequency efficiency. This NOMA system utilizes power domain to improve the performance of multiple access. Signal detection of a near user is operated by successive interference cancellation (SIC). With SIC, the near user cancels out the signal of far user and decodes its own data. Thereafter, the near user drops the cancelled data if SIC is successful. On the other hand, the far user still needs that the far user data may be retransmitted in case of far user reception failure, i.e., no-acknowledgement. Therefore, retransmission to the far user via the near user is efficient when the near user reuses its cancelled data. In this paper, we investigate more efficient way to conduct hybrid automatic repeat request (HARQ) in NOMA. If the SIC procedure of near user is successful, there is an effective approach to recycle the interference-cancelled data. This concept contains full duplex MIMO technique on near user to support the far user. It is found that the proposed retransmission method provides improvements in view of outage probability, symbol error rate (SER), and throughput of far user.

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.

This paper studies an unmanned aerial vehicle (UAV)-enabled multiple access channel (MAC), in which multiple ground users transmit individual messages to a mobile UAV in the sky. We consider a linear topology scenario, where these users locate in a straight line and the UAV flies at a fixed altitude above the line connecting them. Under this setup, we jointly optimize the one-dimensional (1D) UAV trajectory and wireless resource allocation to reveal the fundamental rate limits of the UAV-enabled MAC, under the users' individual maximum power constraints and the UAV's maximum flight speed constraints. First, we consider the capacity-achieving non-orthogonal multiple access (NOMA) transmission with successive interference cancellation (SIC) at the UAV receiver. In this case, we characterize the capacity region by maximizing the average sum-rate of users subject to rate profile constraints. To optimally solve this highly non-convex problem, we transform the original speed-constrained trajectory optimization problem into a speed-free problem that is optimally solvable via the Lagrange dual decomposition. It is rigorously proved that the optimal 1D trajectory solution follows the successive hover-and-fly (SHF) structure. Next, we consider two orthogonal multiple access (OMA) transmission schemes, i.e., frequency-division multiple access (FDMA) and time-division multiple access (TDMA). We maximize the achievable rate regions in the two cases by jointly optimizing the 1D trajectory design and wireless resource (frequency/time) allocation. It is shown that the optimal trajectory solutions still follow the SHF structure but with different hovering locations. Finally, numerical results show that the proposed optimal trajectory designs achieve considerable rate gains over other benchmark schemes, and the capacity region achieved by NOMA significantly outperforms the rate regions by FDMA and TDMA.

Wireless powered sensor networks (WPSNs) have emerged as a key development\ntowards the future self-sustainable Internet of Things (IoT) networks. To\nachieve a good balance between self-sustainability and reliability, partially\nWPSNs with a mixed power solution are desirable for practical applications.\nSpecifically, most of the sensor nodes are wireless powered but the key sensor\nnode adopts traditional wire/battery power for reliability. As a result, this\npaper mainly investigates optimal design for the partially WPSNs in which\nsimultaneous wireless information and power transfer (SWIPT) is adopted in the\ndownlink. Two scenarios with space division multiple access (SDMA) and time\ndivision multiple access (TDMA) in the uplink are considered. For both the\nSDMA-enabled and TDMA-enabled partially WPSNs, joint design of downlink\nbeamforming, uplink beamforming and time allocation is investigated to maximize\nthe uplink sum rate while guaranteeing the quality-of-service (i.e., satisfying\nthe downlink rate constraint) at the key sensor node. After analyzing the\nfeasibility of uplink sum rate maximization problems and the influence of the\ndownlink rate constraint, semi-closed-form optimal solutions for both\nSDMA-enabled and TDMA-enabled WPSNs are proposed with guaranteed global\noptimality. Complexity analysis is also provided to justify the advantage of\nthe proposed solutions in low complexity. The effectiveness and optimality of\nthe proposed optimal solutions are finally demonstrated by simulations.\n