A low complexity physical-layer network coding scheme for cellular two-way relaying systems

In this paper we present a new simple cooperative relaying scheme. The proposed scheme is compared with simple cooperative schemes with virtual orthogonal space time block coding (OSTBC) and quasi orthogonal space time block coding (QOSTBC). Every of these three schemes includes one base station with two antennas, two relay stations each with a single antenna and one mobile station with a single antenna. The aim of the proposed scheme is to preserve, as much as it is possible bit error rate (BER) performance of the cooperative scheme with virtual OSTBC, but with increased code rate. It is shown that the presented scheme obviously outperforms simple cooperative scheme with virtual QOSTBC, while in comparison with simple cooperative scheme with virtual OSTBC has very similar BER performance and increased code rate.

This paper presents a bit error rate (BER) performance analysis of vehicular communication systems (VCS) based on the IEEE 802.11p standard assuming velocity variations of the mobile stations (MSs). To that end, we propose a novel Monte Carlo vehicle-to-vehicle (V2V) fading channel simulator that takes into account the accelerated motion and trajectory variations of the MSs. On the grounds of the proposed channel simulator, we assess the impact of the MSs' velocity variations on the system's BER performance. We assume that the channel state information is obtained following the least-squares (LS) channel estimation techniques that are commonly implemented in commercial off-the-shelf WiFi devices. The results show that the velocity variations have in general a slight impact on the system's BER performance. However, the performance is aggravated as the data frame length or the relative speed increases. The simulation framework presented in this paper can be used as a benchmark to evaluate the performance of the emerging VCS in safety critical scenarios.

This work proposes a new adaptive pilot pattern used for pilot arrangement at the mobile station and a new channel estimation at the base station. It addresses the bit error rate (BER) performance optimization of wireless channel estimation in massive multiple-input multiple-output systems. First, we propose a new adaptive pilot pattern (APP) that offers a lower BER than the conventional pilot patterns. Then, we suggest a new channel estimation algorithm based on the APP. It is called the shifted APP-channel estimation (SACE). As a result, APP guarantees an optimal BER performance for the different system configurations, channel models, and carrier frequencies. It offers better BER performance than conventional pilot patterns, such as the long-term evolution (LTE) pilot pattern. Moreover, the shifted APP-based channel estimation algorithm solves the error floor caused by the usage of multiple subcarriers. It also offers a signal-to-noise ratio (SNR) improvement that reaches 17 dB at BER $= 10^{-2}$ compared to the conventional minimum mean square error (MMSE) channel estimation.

In a cellular communication system, deploying a relay station (RS) is an effective alternative to installing a new base station (BS). A dual-hop network enhances the throughput of mobile stations (MSs) located in shadow areas or at cell edges by installing RSs between BSs and MSs. Because additional radio resources should be allocated to the wireless link between BS and RS, a frame to be transmitted from BS is divided into an access zone (AZ) and a relay zone (RZ). BS and RS communicate with each other through the RZ, and they communicate with their registered MSs through an AZ. However, if too many MSs are registered with a certain BS or RS, MS overloading may cause performance degradation. To prevent such performance degradation, it is very important to find the proper positions for RSs to be deployed. In this paper, we propose a method for finding the sub-optimal RS deployment location for the purpose of load-balancing and throughput enhancement. The advantage of the proposed method is the efficiency in find the sub-optimal location of RSs and its reliable tradeoff between load-balancing throughput enhancement. Since the proposed scheme finds the proper position by adjusting the distance and angle of RSs, its computational complexity lower than other global optimization approach or learning-based approach. In addition, the proposed scheme is constituted with the two stages of load-balancing and throughput enhancement. These procedures result in the appropriate tradeoff between load-balancing and throughput enhancement. The simulation results support these advancements of the proposed scheme.

This paper addresses channel state information (CSI) estimation in a wireless relay network, which consists of a base station (BS), a relay station (RS), and a mobile station (MS). We propose a method for the BS to obtain the instantaneous CSIs of the three links (BS-RS, BS-MS, and RS-MS links) with minimized overhead. The CSI availability plays an important role for the BS to adapt its transmission strategies to the given channel conditions. Our proposed method exploits the fact that the link condition between fixed BS and fixed RS tends to be stable, and the frequent CSI update is not necessary for this link. In order for the BS to obtain the CSI of the distant link (i.e. RS-MS link), RS amplifies a pilot signal received from MS with a pre-defined amplification factor, and forwards it to BS. This enables the BS to obtain the CSI of the RS-MS link based on the received pilot signal and pre-knowledge on the CSI of BS-RS link. We show by computer simulation that our proposed method can reduce the required overhead for CSI estimation with little degradation on the accuracy of the obtained CSI.

In downlink relay systems, the conventional straightforward relaying scheme named decode-and-forward (DF) protocol is used at relay station (RS) to decode the data received from base station (BS) and forward the decoded data to the mobile station (MS) to improve the spatial diversity gain. However, conventional DF mode is spectral inefficient and not capacity optimal since the wireless channels in BS-to-RS, BS-to-MS, and RS-to-MS links are asymmetric, i.e., different channel qualities are obtained in different links in the practical scenario. In this paper, a distributed layered-modulation scheme is proposed to improve the DF mode performance in the presence of asymmetric links. With this proposed scheme, BS and/or RS transmit/re-transmit a layered modulated signal comprising a higher-order and a lower-order modulation components according to the different channel conditions in BS-to-RS and RS-to-MS links, respectively, and, therefore, the channel capacity of each link can be utilized efficiently. In addition, a two-layer demodulation is proposed at the destination by exploiting the two copies of transmitted packet from BS and RS, respectively. In order to further enhance the decoding performance, a soft combining method, in which the bit Log Likelihood Ratio (LLR) of the signals that received during the broadcast phase and the relaying phase are combined before turbo decoding, is used at MS receiver. Simulation results show that the proposed distributed layered modulation scheme obtains a significant performance gain in terms of block error rate (BLER) compared to the existing DF relaying scheme.

ABSTRACTIn massive MIMO systems, inter-user interference has effect on the transmitted signals, so linear precoding techniques are employed for multiuser transmission channels to remove this inter-user interference. It is very complicated to design a suitable linear precoding technique having low computational complexity, which will give an excellent Bit Error Rate (BER) performance. In this paper, we analyse BER under imperfect Channel-State-Information (CSI) using Zero-Forcing (ZF) linear precoding scheme in the downlink, massive MIMO in Time-Division-Duplex (TDD) mode. We derive the closed-form expressions for BER that are obtained from the new expressions derived for Signal-Interference-Noise Ratio (SINR), and then analysis with different parameters using numerical and Monte Carlo simulated results is carried out in MATLAB under imperfect CSI. It was found that our theoretical analysis agrees well with the simulated results. In our analysis, BER was observed in most cases to be good when the number of Base Station (BS) antennas is large enough to accommodate the served users, but when the number of users grows up, the BER performance degrades depending on how many BS antennas are capable of handling the additional users. Also, increasing the downlink transmit power was found to improve the performance, but it is not an energy-efficient way for massive MIMO.

The IEEE 802.16j mobile multi-hop relay (MMR) is studied to improve throughput, extend coverage, and increase capacity. Mobile relay stations attached to vehicles make arbitrary movements and have interference with other base stations or relay stations, thus lowering service functions. This study sets out to suggest an interference detection and avoidance method and evaluates its performance in order to help introduce a mobile relay station for vehicle mounting in a mobile multi-hop relay network. The proposed approach would be implemented by the addition of MAC management messages at a base or relay station instead of the change of mobile station.

This paper proposes the theoretical derivation method of both the frequency spectrum and the bit error rate (BER) performance for uplink Orthogonal Frequency Division Multiple Access (OFDMA) in the presence of the nonlinear distortion. Since OFDMA has two different subcarrier allocation methods such as localized FDMA (LFDMA) and interleaved FDMA (IFDMA), there is the difference, in terms of the influence of the nonlinear distortion at each mobile station (MS) on the out-band radiation and the BER degradation, between LFDMA and IFDMA. Therefore, it is meaningful to clarify this difference by means of the theoretical approach. The feature of the proposed approach is to represent both the frequency spectrum and the BER performance by the simple series form formula, which enables us to overview these performances without any time-consuming computer simulations. The validity of the proposed formula is confirmed by the agreement with the computer simulation results with the parameters of the number of MSs and the input back-off (IBO).

In this paper, we design a resource allocation (RA) scheme for the downlink of relay-assisted orthogonal frequency division multiple access cellular networks. Our design goal is to maximize the energy efficiency (EE) with minimal signaling overhead and low computational complexity. To alleviate the signaling overhead of channel information, the proposed scheme allocates the resources in a distributed manner, where each relay station (RS) or base station (BS) individually performs a joint subchannel and power allocation for its subordinate users. To increase the cell throughput, the proposed scheme allows the subchannel reuse among RSs and this enhances the EE performance. The proposed scheme is composed of the resource allocation at RS (RS-RA) and the resource allocation at BS (BS-RA). The RS-RA is formulated as an optimization problem that minimizes the consumed power of RS while reusing as many subchannels as possible among RSs. The optimization objective of BS-RA is to maximize the EE of the cell. Simulation results show that the proposed distributed RA scheme achieves remarkably excellent EE performance with small signaling overhead, comparable with the centralized optimal RA scheme aiming at the EE maximization based on full channel information.

In this paper, we consider a multi-hop relay networks in IEEE 802.16j system with the full frequency-reuse capability, in which a frame structure can be asymmetrically divided into two different intervals, one for access zone to base station (BS)/relay station (RS)-mobile stations (MSs) communication and the other for relay zone to BS-RS communication, while the same radio resource is fully reused by every RS in the cell. This paper proposes a frame scheduling algorithm that improves the overall system throughput by reducing waste of radio resource through balancing of resource allocation in each relay station (RS). The proposed algorithm is divided into two stages: first, a boundary between access zone and relay zone is scheduled by BS and determined dynamically; second, traffics that will be retransmitted by automatic repeat request (ARQ) and generated by difference between current and scheduled MCS (modulation and coding scheme) level are scheduled by RS. The simulation results show that proposed algorithm improves the overall system throughput approximately by 35% over a conventional frame scheduling algorithm without any load balancing capability.

A multi-user network code assisted HARQ system with cooperative relay is proposed. Uplink (UL) transmission with multiple mobile-stations (MSs) cooperating with a relay-station (RS) using HARQ is considered. The RS is assumed to he able to successfully monitor and decode the packets transmitted from the MSs to the base-station (BS). The BS partitions the incorrectly decoded packets into groups based on their MS-to-BS channel conditions and feedback this partition to the RS along with the acknowledgement (ACK) or negative acknowledgement (NACK). The RS employs, for each group inside the partition, a network-coded HARQ scheme using packets in that group for subsequent retransmissions. We proposed a dynamic and adaptive partitioning method based on the channel state information at the BS and the corresponding HARQ retransmission schemes. Also, we derived the corresponding low-complexity joint demodulation and decoding structure for this multi-user HARQ scheme. We found via simulations that our proposed scheme can improve the system throughput by around 15% when compared with the simple relay assisted chase combining HARQ system.

The use of wide-band and low-loss fiber-optic feeders to transfer the complex signal processing and control functions from the base station (BS) to a central control station (CCS) in a microcellular system, has attracted a great deal of attention. The optical feeder allows compact and cost-effective base stations, easier channel assignment control, and. flexible communication systems. This paper investigates the simultaneous influence of the effects of the wireless channel such as fading and cochannel interference (CCI) and the effects of the optical channel, like shot noise and intermodulation distortion, introduced by the laser diode on the bit error rate (BER) performance of a fiber-fed microcellular system using the /spl pi/ /4-differential quadrature phase-shift keying (DQPSK) modem scheme. The wireless channel is assumed to be a frequency-selective, slow, and CCI-limited Nakagami fading channel. The BER performance of the system is studied under various channel conditions using an exact model and a simplified model and a comparative study with a nonfiber-fed system is carried out. The tradeoff between the system capacity and the BER performance in fiber-optic microcellular (FOM) systems is also discussed. The results obtained justify the application of fiber-optic feeders as the remoting infrastructure for future microcellular systems.

Relay, which serves to enhance the performance of future communication networks, is one of the most promising techniques for IMT-Advanced systems. The potential performance improvement of relay is investigated in this work. Our investigation consists of two steps. In the first step, to obtain a better understanding of the fundamental properties of relay channels, we conducted outdoor measurements at 2.35 GHz with 50 MHz bandwidth in a typical urban area of China. Three links constituting the relay transmission, i.e., the link between base station and relay station, the link between relay station and mobile station and the link between base station and mobile station were measured by employing a real-time channel sounder. Two main factors that affect the MIMO channel capacity, i.e., the channel gain and effective degrees of freedom, are investigated. The cross-polarization discrimination was obtained by utilizing space-alternating generalized expectation-maximization algorithm. The channel parameters of the three links are statistically analyzed and compared. In the second step, based on the measured data, the performance of different relaying schemes, i.e., amplify-and-forward and decode-and-forward, is evaluated. The impact of RS antenna configuration on the capacity is also analyzed. The measurement and evaluation results reveal that the relay can significantly improve the system coverage and performance.

Relay has been identified as a fundamental feature in LTE-Advanced in order to achieve LTE-A requirements. The conventional straightforward relaying scheme named decode-and-forward (DF) protocol is used at relay station (RS) to decode the data received from mobile station (MS) and forward the decoded data to the base station (BS) to improve the spatial diversity gain. It is not efficient and optimal since the traditional DF scheme has not considered the unequal bit reliability within each QAM symbols. In this paper, a bit rearrangement technique is used at RS to improve the performance of the cooperative relaying system, in which the bit remapping employed at RS is different from the one used at MS. At BS, the soft information combining technique with maximum a posteriori (MAP) is used to demodulate the data before turbo decoding. Simulation results show that the proposed cooperative transmission scheme obtains a significant performance gain in terms of block error rate (BLER) compared to the traditional DF relaying scheme.