Leaky CoaXial (LCX) cable is a line-shaped cable used as antenna for wireless system. Due to its stable and uniform radiation characteristics with changeable shape, LCX cable is largely used for wireless coverage over many linear-cell environments such as shopping mall, tunnel, underground mall or walkway etc. These scenarios usually require location-aware services for many applications. We have investigated many localization methods for wireless system using the proposed bidirectional LCX. The bidirectional LCX can be used as two antennas by input the signal from both sides of the cable. We have investigated the theoretical positioning error bound (PEB) of the conventional LCX. However, for bidirectional LCX, its theoretical PEB and the advantage over conventional LCX are still unknown. This paper will analyze the PEB property and compare it with the conventional LCX usage based on the LCX channel model developed from the Geometrically-Based Single-Bounce (GBSB) model. We give a brief Fisher Information analysis for wireless system using bidirectional LCX-based localization. Then the impact of different LCX configurations on the PEB is evaluated through the Cramér-Rao lower bound.

In recent years, reconfigurable intelligent surface (RIS) technology is stimulating the usage on the field of wireless communication due to its low-cost hardware and powerful functionality. RIS is composed of many unit cells (reflective cells), and each one can be designed to control the phase of input electromagnetic waves. This enables the adjustment of reflected wireless signals towards the desired direction. By leveraging this feature, RIS can significantly enhance link power and capacity by concentrating reflected waves on the receiver. In addition, by controlling the phases of all unit cells, it can increases the total number of different channel patterns or channels, which can be used as the constellations of spatial modulation (SM) and improve the capacity of wireless system. The main purpose of RIS based SM is to find the appropriate set of cell phases to maximize the minimum distance of the constellation points which is an NP-complete problem. In this paper, we will propose a genetic algorithm (GA) based method to find the appropriate set of cell phases. In addition, we divide all cells into two groups for increasing link quality and generating the constellation points of SM respectively. This paper also evaluates the trade-off between link quality and GA-based constellation distance when the ratio of two groups are changed. The evaluated results show that it exists some ‘good’ ratios to make the system has appropriate constellation distance with good link quality.

This paper proposes overloaded multiuser multiple-input-multiple-output (MU-MIMO) that is able to increase network throughput by increasing the number of the signal streams to more than that of receive antennas. The spatial filter is employed at each user for such spatial multiplexing. In addition, the proposed overloaded MU-MIMO applies the non-linear precoding with the lattice reduction for improving the transmission performance with low computational complexity. The use of the non-linear precoding can simplify the receiver configuration where amplifiers and the spatial filters are only needed. Computer simulation shows that the proposed overloaded MU-MIMO can double not only the user throughput but also the network throughput compared with the conventional MU-MIMO based on the block diagonalization (BD). In spite of the superior throughput enhancement, the proposed overloaded MU-MIMO achieves 13 dB better transmission performance than the conventional MUMIMO at the BER of $10^{-4}$.

This paper proposes overloaded MIMO spatial multiplexing that is able to increase the number of spatially multiplexed signal streams despite of the number of antennas on a terminal and that on a receiver. We propose extension of the channel matrix for the increase in the number of the signal streams. We apply QR-decomposition based on the equal gain transform to the extended channel matrix, which is employed to achieve superior transmission performance despite of the increase in the number of the spatially multiplexed streams. The transmission performance of the proposed multiplexing is evaluated by computer simulation. The simulation reveals that the proposed multiplexing can implement 6 stream-spatial multiplexing in a 2 × 2 MIMO system, i.e., the overloading ratio of 3.0. The diversity order of 2 is attained in the MIMO system, despite of the high overloading ratio of 3.0.

This paper proposes an overloaded multiple-input-multiple-output (MIMO) 2-hop network with physical layer network coding for high speed wireless communications. The number of the spatial multiplexed signal streams can be raised to that of the transmit antennas in the proposed network even where the number of antennas on the relay is less than that on the terminals. The proposed overloaded MIMO network applies precoding and relay filtering to reduce computational complexity. Furthermore, we propose a technique to select the best filter among candidates relay filters. The performance of the proposed network is evaluated by computer simulation. The proposed filter selection technique attains a gain of about 1.5dB at the BER of $10 ^{-5}$ in the network where 2 antennas and 4 antennas are placed on the relay and the terminal, respectively. This paper shows that 6-stream spatial multiplexing can be exchanged between the terminals via the relay with 2 antennas.

Leaky Coaxial (LCX) cable is a line-shaped cable with huge number of slots used to transmit / receive wireless signal. Due to its changeable shape and stable and uniform radiation characteristics along cable, it has been largely used for wireless coverage over many scenarios such as linear-cell environments and any irregular shape of coverage. In addition, by opening and closing (On/Off) partial slots, LCX cable can largely increase the total number of different channel patterns, which benefits the capacity increase for LCX system using spatial modulation (SM). However, due to the large number of slots, it is difficult to find an optimal solution in terms of channel patterns set generated from On/Off status of LCX slots, which can be treated as an NP-complete combination optimization problem. In this paper, we propose an efficient channel pattern selection based on genetic algorithm (GA) for 2-by-2 LCX-MIMO system using single LCX.

We consider overloaded communication in multi user-multiple input multiple output (MU-MIMO) systems in order to further increase the capacity of downlink communication to multiple users. Overloaded communication is a case where the number of receiving antennas is smaller than the number of transmitting streams. In the proposed scheme, overloaded MU-MIMO communication is achieved by precoding with a weight matrix generated based on singular value decomposition. In contrast, we attempt to improve the communication characteristics by non-linear precoding (for example Tomlinson-Harashima Precoding (THP)) to reduce the characteristic difference of each stream. In addition, the non-linear precoding uses Lattice-Reduction to optimize the modulo processing. At the receiver, Lattice-Reduction aided Successive Interference Cancellation (SIC) is performed on the transmitted signal. The Lattice-Reduction improves the orthogonality of the channel portion, resulting in lower spatial correlation and reduced noise enhancement. Bit Error Rate (BER) characteristics were calculated by computer simulation, and the precoding characteristics were evaluated and compared. The results showed that the transmission characteristics of the overloaded MU-MIMO system and the non-linear precoding improved the transmission characteristics.

This paper proposes low complexity resource allocation in frequency domain non-orthogonal multiple access where many devices access with a base station. The number of the devices is assumed to be more than that of the resource for network capacity enhancement, which is demanded in massive machine type communications (mMTC). This paper proposes two types of resource allocation techniques, which are named as "CGVS" and "LLRVS", all of which are based on the MIN-MAX approach. CGVS seeks for nicer resource allocation with only channel gains, while LLRVS applies the message passing algorithm (MPA) for better resource allocation. The proposed resource allocation techniques are evaluated by computer simulation in frequency domain non-orthogonal multiple access. Whereas LLRVS achieves only 0.1dB better performance than CGVS in the multiple access with the overloading ratio of 1.5 at the BER of 10−4, CGVS can be implemented with 10−5smaller computational complexity than LLRVS. CGVS attains a gain of about 10dB at the BER of 10−4in the multiple access with the overloading ration of 2.0. The complexity of CGVS is 10−16as small as the conventional technique.

Localization, as a key technology, has promoted various location-based services and applications. It also plays an important role in many novel systems such as the Internet of Things (IoT), smart buildings and houses, and unmanned aerial vehicle (UAV) systems. Different from the requirements for localization technology in the past, today’s indoor localization systems need to provide not only the two-dimensional (2-D) location information of the target but also stable three-dimensional (3-D) information. Most of the existing localization methods in wireless communication consider the communication systems using conventional monopole antennas. However, in many application scenarios such as smart manufacturing factories, the shielding and interference effects of metallic objects on radio waves limit the performance of conventional monopole antennas. It is often necessary to increase the number of access points (APs) with additional complexity and cost to guarantee entire wireless coverage. Leaky coaxial cable (LCX) which can be used as antennas for wireless communication can be employed to solve this problem. As a long and flexible cable, LCX can provide promising wireless coverage for stable wireless communication and localization. This paper proposes a 3-D localization method using multiple LCXs in an indoor environment. The proposal is based on a particle filter algorithm and uses the time of arrival (TOA) of the signal as the indicator for filtering.

This paper proposes a low complexity receiver that outperforms the MLD in overloaded MIMO-OFDM systems. The proposed receiver applies iterative noise cancellation to improve the transmission performance. A low complexity LLR calculation technique is introduced in the proposed receiver. The proposed low complexity iterative non-linear receiver achieves better transmission performance than the MLD with smaller calculational complexity. The performance of the proposed techniques is verified by computer simulation in a 6×3 overloaded MIMO channel. When the reception process is only iterative 2times, the proposed iterative non-linear receiver attains a gain of 0.8dB at the BER of 10−6. The computational complexity is evaluated in terms of the number of additions. The proposed receiver achieves such superior performance with the complexity which is about half as much as conventional soft input decoding with the MLD.

This paper proposes a novel approach to low complexity soft input decoding for lattice reduction-aided MIMO receivers. The proposed approach feeds a soft input decoder with soft signals made from hard decision signals generated by using a lattice reduction-aided linear detector. The soft signal is a weighted-sum of some candidate vectors that are near by the hard decision signal coming out from the lattice reduction-aided linear detector. This paper proposes a technique to adjust the weight adapt to the channel for the higher transmission performance. The transmission performance is evaluated in a 4 x 4 MIMO channel. When a serial interference canceller is used as the linear detector, the proposed technique achieves about 2.0 dB better transmission performance at the BER of 10-5than the decoder fed with the hard decision signals, even though the proposed soft input decoding can be implemented with small additional complexity.

As a key technology, localization has promoted many location-based services and applications. It also benefits various novel systems such as the Internet of Things (IoT), autonomous vehicles, and smart homes and buildings. Smart manufacturing factory, as an important application scenario in Industry 4.0, need effective and stable localization technology as technical support for advanced production. Most of the existing localization methods in wireless communication consider the communication systems using conventional monopole antennas. However, in a factory environment, the influence of metal objects on the shielding and interference of radio waves limits the performance of conventional monopole antennas. It is often necessary to increase the number of access points (AP) with additional complexity and cost to guarantee entire wireless coverage. Leaky coaxial cable (LCX) which can be used as antennas for wireless communication can be employed to solve this problem. As a long and flexible cable, LCX can provide promising wireless coverage for stable wireless communication and localization. This paper is aimed at a particle filter-based localization method using LCX in an indoor environment. The localization scheme uses the time difference of arrival (TDOA) as the indicator for filtering.

This paper proposes a novel interference cancellation technique that keeps radio receivers from periodic interference signals caused by electromagnetic waves emitted from high power circuits. The proposed technique cancels periodic interference signals in the frequency domain, even if the periodic interference signals are drifted in the time domain. We propose a drift estimation based on a super resolution technique such as ESPRIT. The proposed technique employs a linear filter based on the minimum mean square error criterion with assistance of the estimated drifts for the interference cancellation. The performance of the proposed technique is confirmed by computer simulation. The proposed technique achieves a gain of more than 40 dB at the higher frequency index.

This paper proposes an iterative low complexity soft input decoding with assistance of the lattice reduction for overloaded MIMO. The proposed soft input decoding applies two types of lattice reduction-aided linear filters to estimate log-likelihood ratio (LLR) in order to reduce the computational complexity. A lattice reduction-aided linear with whitening filter is introduced for the LLR estimation in the proposed decoding. The equivalent noise caused by the linear filter is mitigated with the decoder output streams and the LLR is re-estimated after the equivalent noise mitigation. Furthermore, LLR clipping is introduced in the proposed decoding to avoid the performance degradation due to the incorrect LLRs. The proposed decoding achieves about 2dB better BER performance than the soft decoding with the exhaustive search algorithm, so called the MLD, at the BER of 1.0E-4, even though the complexity of the proposed decoding is 1/10 as small as that of the soft decoding with the exhaustive search.

This paper proposes a low density signature-based packet access with phase only adaptive precoding. The proposed access allows multiple user terminals to send their packets simultaneously though only one antenna is put on terminals and on an access point, in order to increase network throughput. The proposed phase only adaptive precoding improves the transmission performance by rotating the transmission signal phase. This paper proposes a criterion that defines the optimum rotation angle, and actual two techniques to estimate the angle. When 6 packets are transmitted in 4 time slots, the proposed adaptive precoding attains about a gain of 4dB at the BER of 10-4in a single input single output Rician fading channel, i.e., overloading ratio is 1.5.

This paper proposes a novel receiver with virtual channels for overloaded MIMO systems, where the number of spatial multiplexing streams is more than that of receive antennas. We propose extended rotation matrices used for the receiver in order to make the receiver performance flexible in terms of complexity and detection performance. A lot of the extended rotation matrices can be formed, even if the size of the rotation matrix is fixed. This paper proposes to select the optimum extended rotation matrix adaptive to the overloaded MIMO channel for further performance improvement. The performance of the proposed receiver with the extended rotation matrix is evaluated by computer simulation. It is shown that the the optimum extended rotation matrix selection attains 2dB of a gain at BER of 1CP3 in the proposed receiver.

Bi-directional relaying has been demonstrated to raise transmission throughput intensively as large as twice in throughput by applying physical layer network coding (PNC) when a pair of terminals exchange information via relay. With the aim to enhance the performance of relay system based on decode-and-amplify (DF) strategy, we propose a PNC scheme using Tomlinson-Harashima precoding (THP). Assuming the same broadcast scheme, our proposed scheme shows better performance than conventional linear precoding scheme. To reduce the transmission power without increasing bit error rate (BER), we further introduce a power controlling (PC) structure. It is proved that the transmission power and BER can both be reduced with the power controlling method.

A transmission experiment of a multi-user MIMO system with user selection and linear spatial precoding is conducted and the results are reported. As a low-complexity user selection algorithm, the chordal distance-based user selection (CDUS) algorithm is employed. The testbed used in the experiment is implemented by taking full advantage of the software-defined radio. An amplify-and-forward-based simple channel estimation method is adopted. As a result of the experiment in a conference room, the CDUS algorithm improved both the power efficiency and the interference suppression accuracy compared to the round-robin user selection.

This paper proposes a novel heterodyne multiband multiple-input multiple-output (MIMO) receiver with baseband automatic gain control (AGC) for cognitive radios. In the receiver, the analog baseband AGC is introduced to avoid the baseband signals exceeding the voltage reference of analog-to-digital converters (ADCs). This paper proposes a novel technique to estimate the analog devices imperfection in the heterodyne multiband MIMO receiver with the baseband AGC. The proposed technique does not require any high precision analog devices. The performance of the proposed receiver is verified by using computer simulations. As a result, the required resolution of the ADC is nine bits in the proposed receiver. Moreover, the proposed receiver has less computational complexity than that with the baseband interference cancellation unless a frequency band is changed once in nine packets or less.

This paper proposes a novel radio frequency (RF) devices imperfection estimation scheme for the heterodyne multiband multiple-input multiple-output (MIMO) receiver with the baseband automatic gain control (AGC) for cognitive radios. It is quantitatively shown that the proposed estimation scheme allows analog-to-digital converters (ADCs) with lower resolution to be applied to the receiver than the conventional estimation technique. Also, the proposed scheme is shown to attain rapid convergence, and to keep superior bit error rate (BER) performance in spite of the power of image-band interference. It is shown that the proposed estimation scheme makes the receiver with 8 bits ADCs attain the BER performance even in the presence of strong image-band interference, e.g., CIR=-40 dB.

A practical and efficient vector quantization called partitioned vector quantization (P-VQ) based non-linear precoder for MIMO downlink broadcasting channels has been analyzed in this paper. P- VQ has been found to be an efficient way of reducing the memory requirements and search complexity in conventional VQ systems, especially for large MIMO. Simulation results reveal that P-VQ technique can enhance the overall quantization performance in terms of achieved capacity, bit error rate (BER) at a cost of reasonable additional complexity under certain feedback budgets. Tomlinson-Harashima precoding (THP), a power and complexity efficient precoding technique along with data dependent vector perturbation (VP) has been employed to meet the power constraint requirements of our system. Least-square (LS) channel estimation is performed at the user terminals to acquire their channel state information (CSI).

In this paper, the end-to-end packet error rate (PER) performance of a space-time block code (STBC) based multi-hop cooperative relaying system is discussed. This system consists of a source, a destination, and two STBC based cooperative relays in each hop. These relays decode their received packets and forward the packets only when no error is found. In this system, there are conditions where the end-to-end PER performance improves with the number of hops. The theoretical end-to-end PER performance of this system have been derived analytically. However, in real-world wireless systems, various practical issues, e.g., timing synchronization and imperfect channel estimation, have a large impact on the performance. To confirm the end-to-end PER performance of this system in actual setup, an in-lab experiment using a fading emulator and four transceivers is performed under Rayleigh fading environment. The experimental results clarify the PER performance of the STBC based multi-hop cooperative relaying system. In addition, the theoretical PER performance is also verified from the experimental results.

Cognitive radios are of interest because they are capable of high frequency utilization efficiency. Multiband multiple-input multiple-output (MIMO) receivers based on heterodyne reception have been proposed for use in cognitive radios. This paper proposes a reduced-complexity multiband MIMO receiver that can achieve high performance by correcting the imperfection of the Hilbert transformer in the intermediate frequency (IF) band. However, the imperfection of the analog devices in the feedback loop causes poor performance. Therefore, a scheme for correcting the imperfection of the analog devices is proposed.

In this paper, implementation of a multi-user MIMO experimental system is presented. Linear spatial precoding and a simple two- way channel estimation technique are adopted in the experimental system. In-lab and field transmission experiments are carried out and the performance is evaluated. The impact of channel estimation error under average channel gain discrepancy between two mobile stations is analyzed by means of computer simulation. It is shown that channel estimation error has a greater influence on the mobile station with greater average channel gain.

In this paper, we propose a receiver using the concept of a "virtual channel" and Turbo codes for multiuser multiple-input multiple-output (MU-MIMO) systems with cooperating transmitters. In order to reduce feedback information from receivers, a precoding method with reduced channel state information (CSI) is needed. Although signals interfere with each other in such a system, the proposed receiver enables high-speed transmission by detecting signals iteratively. In the proposed iterative scheme, soft information is exchanged between virtual channel detectors and Turbo decoders to improve the bit error rate (BER) performance. We evaluate the performance of the proposed receiver in systems with two transmitters, each equipped with four antennas, and two receivers, each equipped with two antennas. The results show that the proposed receiver can improve the system performance owing to the iteration scheme.

Cognitive radios are of interest because they are capable of high frequency utilization efficiency. In a cognitive radio, multiband receivers are required to make use of unused frequency bands. On the other hand, MIMO (multiple-input multiple-output) spatial multiplexing is also used to increase transmission capacity. This paper proposes a multiband MIMO receiver with ordered successive detection based on heterodyne reception. Because the use of an RF-BPF (radio frequency-bandpass filter) with a wide pass band is required in the receiver for multiband reception, the heterodyne receiver suffers from image-band interference. Therefore, the proposed receiver is designed not only to detect spatially multiplexed signals but also to suppress image-band interference. Computer simulation shows that the proposed receiver achieves superior BER performance even in the presence of strong image-band interference signals.

In this paper, we propose a virtual layered space-frequency receiver with an ordered successive detector for multiuser multiple-input multiple-output (MU-MIMO) systems where multiple transmitters cooperate with one another. The proposed receiver enables high-speed transmission in the systems even if the transmitters know only partial channel state information (CSI). Actually, the receiver shows such superior performance when the concept of "virtual channel" is applied to cooperative MU-MIMO systems. Moreover, we propose an iterative detection scheme for the receiver; in this scheme, some signals from the Viterbi decoder are fed back to the ordered successive detector. The proposed iterative scheme helps improve the transmission speed when the number of cooperating transmitters is increased. We evaluate the performance of MIMO systems in which the transmitters have four antennas each and two users have two antennas. The receiver can double the transmission speed at the cost of 3 dB in Eb/N0at a BER of 10-4. Furthermore, the receiver can triple the transmission speed at the cost of 7 dB in Eb/N0at a BER of 10-4. When the system has three transmitters, we observe an error floor. However, the proposed iterative method can suppress the error to a value below BER = 10-7.

This paper considers two-hop wireless systems employing network coding and a carrier sense multiple access (CSMA) protocol. Network coding is a recent and highly regarded technology for the capacity enhancement of multiple unicast and multisource multicast networks. The two-hop wireless CSMA systems are often involved with the hidden node problem, but the impact of the hidden nodes on network coding has not been analyzed in theory. This paper provides explicit expressions of the throughput for single-relay two-hop wireless CSMA systems both without and with network coding. The throughput can be obtained from these expressions for given system parameters even when end nodes via the relay node are hidden each other. Furthermore it is shown that the transmit probability of the relay node is a design parameter that is crucial for maximizing the achievable throughput for CSMA systems with network coding. It is clarified that the throughput for CSMA systems can be enhanced as compared with that for slotted ALOHA systems in case of non-hidden end nodes whereas it deteriorates considerably in case of hidden end nodes.

In this paper, we introduce, a new method named “Complexity Reduction Method based on Compensation Distance” in order to reduce the complexity of the detection in virtual layered space-time receivers in multiple-input multiple-output (MIMO) systems. Moreover, this method is practical even when the number of transmitting streams is greater than that of receiving antennas. Computer simulations indicate that the proposed method can be used to reduce the complexity of detection to approximately 20% in [8×4] (the transmitter is equipped with 8 antennas and the receiver is equipped with 4 antennas) systems.

A novel method is proposed in this paper to cancel the image-band interference for multi-mode/band receivers with baseband AGC. The Hilbert transformer, which plays an important part in heterodyne multi-mode receivers described here, has the imperfection which results in image-band interference in baseband, causing severe deterioration of transmission performance. The method proposed here cancels the image-band interference by estimating and canceling imperfection of the analog Hilbert transformer consisting of the phase error and the amplitude error by correlation matrices calculation. Furthermore, filtering is employed here to improve the estimation accuracy. This paper also shows the error estimation performance of the proposed method and the BER performance of the interference cancellation by computer simulation under the circumstance of CIR =-20 dB, and compares them with that of the conventional method.

In this study, we develop a virtual layered space-frequency communication architecture. This architecture enables the decoding of transmitted OFDM (orthogonal frequency division multiplexing)-QPSK signals even if the number of antennas at the transmitter is twice the number of antennas at the receiver over multipath fading channels. Furthermore, we propose two detection schemes called "hard replica" and "soft replica." In addition, in order to improve the performance of this architecture, we propose an iteration in which the receiver decodes the detected signals; through such iterations, this architecture can obtain path diversity and achieve high performance. When the transmitter has four antennas and receiver has two antennas, the proposed architecture achieves BER of 8 × 10-4using the soft replica at Eb/N0= 15 dB. Furthermore, by performing more iterations, it provides additional gains of 3 dB. The performance of the proposed architecture is verified using computer simulations.

This paper deals with two representative bidirectional traffic cases in two-hop wireless relay access systems employing network coding and a slotted ALOHA protocol. Network coding is a recent and highly regarded technology for capacity enhancement of multiple unicast and multisource multicast networks. The relay nodes are generally involved with unbalanced multidirectional traffic, but the impact of the unbalanced traffic on network coding has not been analyzed. This paper provides closed-form expressions for the throughput and packet delay for two-hop bidirectional traffic cases both with and without network coding even if the buffers on nodes are unsaturated. The analytical results are mainly derived by solving queueing systems for the buffer behavior at the relay node. The results show that the transmission probability of the relay node is a design parameter that is crucial for maximizing the achievable throughput of slotted ALOHA systems with network coding in two-hop bidirectional traffic cases.

In this study, we develop a virtual layered space-frequency communication architecture. This architecture enables the decoding of transmitted OFDM (Orthogonal Frequency Division Multiplexing)-QPSK signals even if the number of antennas at the transmitter is twice the number of antennas at the receiver over multipath fading channels. Furthermore, in order to improve the performance of this architecture, we propose an iteration with prior probability in which the receiver decodes the detected signals; through such iteration, this architecture can obtain path diversity and achieve high performance. When the transmitter has four antennas and receiver has two antennas, the proposed architecture achieves BER of 8×10-4at Eb/N0= 13.5 dB. Furthermore, by performing more iterations, it provides additional gains of 5 dB. The performance of the proposed architecture is verified using computer simulations.

This paper proposes a novel receiver architecture named as "Virtual layered space time reception" for MIMO wireless communication systems. In the proposed reception architecture, a transmission signal is regarded to comprise a sign signal and fractional phase shift. The phase shift combined with wireless channels are dealt as a virtual channel. Then, the sign signal which is assumed to be transmitted over the virtual channel is detected by a serial interference canceler (SIC) like V-BLAST. The receiver based on the proposed architecture can detect more data streams than the number of received antennas, even though the architecture applies the SIC. This means that the receiver based on the proposed architecture can form more communications channels between the transmitter and the receiver than the number of received antennas. Therefore, the proposed architecture has potential of increasing channel capacity. Actually, computer simulation result shows that the proposed receiver attains superior performance even when the number of transmit antenna is twice as many as that of the received antennas.

We propose an architecture which reduce the circuit size to concurrently cancel co-channel interference and image- band interference. We adopt analogue Hilbert transformers to cancel image-band interference and adaptive array antennas to cancel co-channel interference. Furthermore, we can miniaturize the receiver by mixing all signals at the IF stage. We also show performance of the proposed system by computer simulation. As a result, image-band interference caused by some imperfection of Hilbert transformer can be completely canceled. Moreover, co-channel interference can be simultaneously canceled.

This paper deals with two representative unbalanced traffic cases for two-hop wireless relay access systems employing network coding and a slotted ALOHA protocol. Network coding is a recent and highly regarded technology for capacity enhancement with multiple unicast and multisource multicast networks. We have analyzed the performance of network coding on a two-hop wireless relay access system employing the slotted ALOHA under a balanced bidirectional traffic. The relay nodes will generally undergo this unbalanced multidirectional traffic but the impact of this unbalanced traffic on network coding has not been analyzed. This paper provides closed-form expressions for the throughput and packet delay for two-hop unbalanced bidirectional traffic cases both with and without network coding even if the buffers on nodes are unsaturated. The analytical results are mainly derived by solving queueing systems for the buffer behavior at the relay node. The results show that the transmission probability of the relay node is a design parameter that is crucial to maximizing the achievable throughput of wireless network coding in slotted ALOHA on two-hop unbalanced traffic cases. Furthermore, we show that the throughput is enhanced even if the traffic at the relay node is unbalanced.

This paper deals with a simple but essential two-hop wireless relay network employing network coding and a slotted ALOHA protocol. Network coding is a recent and highly regarded technology for capacity enhancement on multiple unicast and multisource multicast networks. However, the performance of network coding on wireless relay networks employing random access protocols has not been analyzed. This paper provides closed-form expressions for the throughput and delay on two- hop wireless relay networks both with and without network coding from a theoretical perspective of the slotted ALOHA protocol. The analytical results are derived by solving queueing systems for the buffer activity at the relay node. The results show that the transmission probability of the relay node is a design parameter that is crucial to maximizing the achievable throughput of slotted ALOHA with network coding on a two-hop wireless relay network. Furthermore, this paper clarifies that the throughput is enhanced by controlling the transmission probability of the relay node such that it has considerable opportunity for network coding.

This paper proposes a novel receiver structure based on a heterodyne receiver for multimode/multiband communications. Although the proposed receiver can demodulate RF (radio frequency) signals of any carrier frequency, the receiver can be implemented with only an RF receiver chain. This is made possible by widening bandwidth of the receiver front end. Nevertheless, the proposed receiver achieves the theoretical performance even in multipath fading channels, while canceling image-band interference caused by widening bandwidth of the RF front end. Performance of the proposed receiver is verified theoretically and confirmed in computer simulation.

This paper describes measurement campaign conducted in different scenarios of indoor office environment. An ULA antenna array and virtual antenna array were used at receiver and transmitter respectively. The measurement aims to characterize indoor radio propagation characteristics. Results of measurement at 5.2 GHz frequency and 120 MHz bandwidth are discussed that include propagation path loss, time delay spread, angular spread, and spatial correlation.

This paper proposes a novel blind multiuser detection scheme which can be applied for MIMO systems. Even though all algorithms employed are basically blind, the proposed scheme can not only separate each user's signal but also achieve high transmission performance for each user without a priori information of a channel and transmit sequence. Especially, a correlation-based algorithm is proposed in order to avoid ill-convergence which sometimes happens in blind systems. Finally, performance of the proposed scheme is verified by computer simulation.

This paper proposes an application method of MLSE to multibeam interference cancellation, which has superior transmission performance even in severe co-channel interference (CCI) channels with Rayleigh distribution. In addition, it is verified by computer simulation that the proposed multibeam interference canceller attains an excellent performance in multipath CCI channels.

A fast channel-estimation scheme for adaptive maximum-likelihood sequence-estimation (MLSE) equalizers called the orthogonal-transformed variable-gain least mean squares (OVLMS) algorithm is proposed. This algorithm requires only as many operations as the least mean squares algorithm in spite of its excellent performance. Furthermore, an operational complexity reduction method is proposed in which the orthogonal matrix is reconfigured as eigenvectors with valid eigenvalues. The OVLMS algorithm is theoretically analyzed and is shown to have both a fast acquisition and a good tracking performance. An equalizer using OVLMS (OVLMS-MLSE) experimentally attains a 5-dB improvement in bit-error rate (BER) performance at BER of 1.0/spl times/10/sup -4/ over coherent detection. The OVLMS-MLSE is found to be free of the degradation caused by sampling phase error. Finally, the OVLMS-MLSE equalizer is experimentally verified to synchronize within five symbols.