Recent technological advances with multiple antennas enable various options in rejecting interference in wireless communication systems. Multi-hop full-duplex (FD) multiple-input multiple-output (MIMO) relaying is coping with two kinds of interference: the self-interference (SI) from the transmitter (Tx) to the receiver (RX) at the same communication node as well as the crosstalk interference (CI, i.e., inter-relay interference) from the neighbor nodes. Regarding to the MIMO layout for rejecting the interferences, four cases are possible according to whether the precoder in Tx or the decoder in Rx try to reject the interferences. We in this paper provide outage probability for the multi-hop MIMO FD amplify-and-forward relaying according to the MIMO layouts and compare their outage performance with numerical investigation. The result shows that it is better to distribute the interference rejection capability between Tx and Rx than to let either of Tx and Rx remove both SI and CI.

Two-path successive relaying scheme is designed to restore the spectral inefficiency due to a half-duplex constraint. When not operating in orthogonal channels, the relay pair used in successive relaying scheme interferes each other. This inter-relay interference degrades the outage performance of the successive relaying scheme significantly. So, the zero forcing beamforming (ZFB) has been proposed to remove the inter-relay interference. But using ZFB (U-ZFB) does not always guarantee better performance than not using ZFB (N-ZFB) due to a loss of diversity gain. In this paper, we propose the two-path successive relaying with threshold-based opportunistic ZFB where only inter-relay interference channel information is available and switching-decision is made by comparing the inter-relay interference with a threshold to be determined. We provide optimal thresholds at each relay. Numerical results show that the outage probability of the proposed two-path successive relaying with threshold-based opportunistic ZFB is better than the outage probabilities of U-ZFB only and N-ZFB only and give insights.

This work investigates a simultaneous wireless information and power transfer (SWIPT) system for cognitive radio systems with average energy harvesting (EH) constraint. We propose two transmission schemes controlled by power control (PC) and transmission probability (TP), respectively. Numerical result gives outage probability between the two schemes.

In this study, the authors investigate a maximum incentive that a primary user (PU) can charge a secondary user (SU) on SU's power consumption devoted to delivering its own signal. As a constraint, the PU also should achieve its data rate at a predefined level. Working as a half‐duplex relay, SU hears PU's signal in the first phase and sends its own signal superimposed on PU's signal in the second phase. SU optimises power allocation between the two signals in the second phase, accounting for the expense‐benefit trade‐off in sending its own signal. Depending on SU's receiver mode or the number of SU's receiving nodes, SU's decision on power allocation is differently optimised. The authors also provide optimal incentive for PU by optimal pricing for different occasions. The optimality is proved in this study. Since the optimality is purchased in practice when PU has perfect knowledge of the SU's response on the PU‐issuing price, the authors also propose an efficient interactive price‐searching protocol between distributed PU and SU. Numerical investigations are given to verify and illustrate the optimality of the proposed price as well as the protocol.

The aim of this paper is to design a bandwidth-efficient multiuser network. We consider a wireless sensor network where a relay helps multiple source-destination pairs which require a minimum data rate. The relay helps communication pairs in probabilistic manner during relaying slots. In the proposed scheme, the relay does not need orthogonal channels (time slots) as many as the number of source-destination pairs but the channels are shared by the relay with some probability. We optimize the slot-sharing ratio to maximize the expected sum rate while guaranteeing the minimum rate for a given number of relaying slots. Numerical examples show that the proposed relaying scheme improves the expected data rate even though the number of relaying slots is less than the number of source-destination pairs.

We propose a cognitive relaying protocol with primary multicasting systems, where a primary transmitter broadcasts a common message to K licensed primary receivers. It typically adjusts its transmission rate to the user suffering from the worst channel condition in order to serve all the users simultaneously. In the limit of a large number of multicast receivers, cooperation is shown to effectively overcome this problem. In this paper, an unlicensed secondary system acts as a relay for the primary receivers. Furthermore, the secondary system achieves spectrum sharing by superimposing the secondary transmission on primary signals. We show that there exists a power allocation threshold above which the cognitive relaying protocol is able to provide better (or at least an equal) outage performance for the primary system and, at the same time, to enable the secondary system to have an opportunity to access the spectrum.

In cognitive radio networks, cognitive secondary users (CSUs) can interfere with the primary users (PUs) when they falsely occupy the PU's licensed spectrum. If CSUs in transmission temporarily form a cooperative relaying network, the interference from CSUs to PU can be reduced due to the cooperative diversity. In this paper, the outage performance as well as the achievable diversity order of opportunistic relaying used for cooperative CSUs is investigated. The cooperative relaying network of CSUs is referred to opportunistically relayed cognitive secondary network (ORCSN). Exact outage probabilities and then the diversity order by high SNR approximation are provided under Rayleigh and Nakagami-m fading channels, respectively. It is shown that a spectrum-sensing method used by the CSUs plays an important role in determining the diversity order in ORCSN. Under Rayleigh fading channels, a cooperative sensing enables ORCSN to achieve the full diversity order but a distributed sensing provides the diversity order smaller than one. Under Nakagami-m fading channels, the achievable diversity order is restricted by the Nakagami channel parameters between the PU and the CSUs and also depends on the sensing method. Moreover, the full diversity order can be achieved by a proper selection of the threshold used for spectrum sensing. Numerical investigation is also provided and used to verify the analysis.

This letter provides an exact and optimal power allocation for a sensor network that consists of multiple sensor-destination pairs and a single relay. The objective of the power allocation is to minimize the sum of transmitting powers by the sensors that have a signal-to-noise-ratio (SNR) constraint. After checking the feasibility of power allocation, an optimal solution is provided using Karush-Kuhn-Tucker (KKT) condition. With numerical investigation, the optimality of the proposed solution is illustratively verified and it is also shown that the extent of reduction in the sum-power consumption achieved by introducing the relay depends on the available relaying power and the number of sources.

Combining a dual-hop relaying with multi-input multi-output (MIMO) transmission is a natural extension to overcome the channel impairments. Transmit beamforming (TBF) and maximal ratio combining (MRC) are widely accepted ones, which maximize the signal-to-noise ratio (SNR) at the receiver when channel state information is available. With these methods, there are four possible combinations in constructing dual-hop transmission: TBF-TBF, MRC-MRC, MRC-TBF, and TBF-MRC, respectively. We provide optimal amplify-and-forward (AF) weights at a relay, which maximize the end-to-end SNR for the four systems, respectively, and show the equivalence of the four systems in terms of the SNR. Using relaxed AF weights from the optimal ones, we provide a probability density function (PDF) and a moment generating function (MGF) for the end-to- end SNR per bit with an assumption of an equal number of diversity branch for each hop, which is used to obtain the BER performance for M-ary QAM and PSK constellations, respectively. Numerical results show that the BERs with the relaxed AF weights provide tight lower bounds for those with optimal AF weights. We also compare the BER performance of above AF relaying with that of dual-hop decode-and-forward (DF) relaying.

In this letter, we study outage performance of opportunistic single relay selection (OSRS) in decode-and-forward (DF) relaying with unequal-power co-channel interferers under Rayleigh fading channels. With the interferers, signal-to-interference-plus-noise ratio (SINR) may not be so great when the interferers also transmit signals at a power level similar to the source. In this case, high signal-to-noise ratio (SNR) approximation often used in outage analysis is not suitable for giving an adequate outage expression. We provide an exact and closed-form outage expression. And using asymptotic analysis, we show that OSRS still achieves full diversity gain in the presence of a finite number of interferers whose transmission powers are finite. When a finite number of interferers also transmit signals at the power level proportional to the source, we show that the asymptotic outage decreases log-linearly as the density of nodes increases. Finally, we show that when the number of interferers is proportional to the node density, the higher density, though creating the greater number of potential relays, does not necessarily contribute to improving the outage performance but deteriorates the performance.

In this letter, we prove that decouple-and-forward (DCF) relaying for dual-hop orthogonal space-time block code (OSTBC) transmissions achieves the maximum diversity order attainable by dual-hop MIMO relaying systems. Decoupling at the relay transforms received OSTBC signals into independent and maximal-ratio combined single-input single-output (SISO) signals, which provides the receive diversity gain, and also enables the relay to use OSTBCs again so as to achieve the transmit diversity gain. In obtaining the diversity order, DCF relaying needs a coherence interval of the length of OSTBC transmissions, which is shorter than the requirement assumed in other works that provide the maximum diversity. Numerical results are also presented to verify the proof and give an insight to the relationship between the diversity order and antenna configurations.

In DS-CDMA systems coherent detection is usually adopted by adding or multiplexing redundant pilot signals with voice or data traffic. The pilot signals need additional transmit power but, at the same time, decrease the power used for traffic channel through facilitating channel estimation, which reduces the bit energy-to-noise density ratio (Eb/No) required for delivering the traffic signals. The interdependency between pilot and traffic channel powers has been analyzed in various studies, but has not yet been exploited in existing power control methods. In this letter, we provide a method of using the interdependency to adjuIn DS-CDMA systems coherent detection is usually adopted by adding or multiplexing redundant pilot signals with voice or data traffic. The pilot signals need additional transmit power but, at the same time, decrease the power used for traffic channel through facilitating channel estimation, which reduces the bit energy-to-noise density ratio (Eb/No) required for delivering the traffic signals. The interdependency between pilot and traffic channel powers has been analyzed in various studies, but has not yet been exploited in existing power control methods. In this letter, we provide a method of using the interdependency to adjust pilot power in the context of the existing power control algorithms, and prove its convergence and that it reduces the total transmit power.st pilot power in the context of the existing power control algorithms, and prove its convergence and that it reduces the total transmit power.

We present a study on the outage probability of multihop wireless communication systems with multiple-input multiple-output (MIMO) link based on the transmit antenna selection and the maximal-ratio combining (MRC) at the receiver. A nonregenerative system (NS) is investigated with an ideal amplifying gain. MIMO channels are assumed in uncorrelated Rayleigh fading.We derive a moment generating function (MGF) of the reciprocal of the end-to-end signal-to-noise ratio (SNR) and obtain a closed-form approximation on the outage probability through the numerical inversion of a Laplace transform. Numerical results show that the presented outage is exactly matched with the outage probability when assuming the ideal relay gain. For more practical gains, the result is shown to be a lowerbound that gets tight at high average SNR as well as for a small number of hops and/or of antennas. We also compare the outage probabilities of nonregenerative MIMO relaying with a regenerative counterpart for multiple hops.

In multiuser multiple-input-multiple-output (MIMO) downlink channels, zero-forcing beamforming (ZFBF), though it is simpler than dirty-paper coding (DPC), has been shown to achieve an optimal sum-capacity growth as the number of users goes to infinity. However, the result is based on the assumption that perfect channel information at the transmitter from all the users is known, which is prohibitive especially for a large number of users due to feedback congestion. In this case, wisely preventing the users with poor channel quality from sending the feedback might relieve the burdensome feedback load, which is often called quality-based channel state reporting (QBR). In this letter, we prove ZFBF with QBR also can achieve the asymptotic optimal growth. With numerical investigations, the optimality is confirmed. In addition, we numerically show how much feedback burden can be reduced by QBR at a negligible cost of the sum-capacity.

Variable-rate space-time block codes (vr-STBCs) without any feedback can support different transmission rates and unequal error protection (UEP) which are needed for multimedia communications. Assuming necessary feedback, in this paper, we introduce two simple joint adaptive modulation and power allocation (AMP) methods for vr-STBCs so as to maximize the total throughput under constraints of transmit power limit and bit error rate (BER) requirements: tightest SER constraint method and iterative method. The tightest symbol error rate (SER) constraint method, which uses tightest SER constraints to guarantee the BER constraints for every modulation orders, is simple but gives a low bound for optimum capacity, and the iterative method gives local optimum capacity with somewhat higher complexity than the former one. Numerical results show that both proposed schemes can enhance the performance of existing vr-STBCs by achieving greater throughput as well as satisfying BER requirements. Moreover, we can see that the capacity loss caused by the tightest SER constraint is not serious comparing to the iterative one, and the iterative method doesn't increase the calculational complexity seriously. We can see that the proposed AMP schemes show more throughput gain as diversity order is decreasing, comparing to the conventional ones, since the proposed adaptive schemes can bring more gain as the channel fluctuation becomes greater.

In this letter, a BER study is presented for the end- to-end performance of dual-hop wireless communication systems employing transmit diversity with orthogonal space-time block codes (OSTBCs), where a nonregenerative or regenerative relay is equipped with a single antenna operating over flat Rayleigh fading channels. More specifically, we provide probability density functions (PDFs) and moment generating functions (MGFs) for the end-to-end SNR of the dual-hop OSTBC transmissions and then present its BER performance overM-ary QAM and PSK modulations, respectively. Numerical investigation shows that the analytic BER provided in the letter makes an exact match with the simulation result in various multiple-antenna transmission scenarios. The result also shows how the number of antennas equipped at the source and destination affects the end-to-end performance.

The closed-form exact bit error rate (BER) expressions of generalized orthogonal space-time block codes (OSTBCs) are first derived for quadrature amplitude modulation (QAM) and phase shift keying (PSK) constellations in spatially white Rayleigh multiple input multiple output (MIMO) channels. Then this analysis is generalized to arbitrarily spatially correlated MIMO channels. Based on the BER analysis, the transmission power of the generalized OSTBCs is optimized such that the average BER is minimized. Furthermore, the optimum transmit power which maximizes the upper-bound of the capacity is derived in closed-form.

In this paper, we prove the asymptotic sum-rate growth like 2 log log N can be achieved in 2 times N times 2 dual-hop relaying systems with 2 transmit antennas at a base station (or a source), N > 2 single receive/transmit antenna relays and 2 destination users with a single antenna. The capacity is achieved when the base station transmits with zero-forcing beamforming and the relays that actively transmit are selected with semi-orthogonal relay selection principle. Since the base station should know the channel information to the relays, the feedback load grows prohibitively large if N rarr infin. To reduce the feedback load from the relays to the base station, we use quality-based channel state reporting (QBR). Numerical results show that the sum-rate achieved by N relays gets close to its multiuser counterpart if the amplifying gain at the relay is large. We also show how QBR is effective in reducing the feedback load when N is large.

In this paper, we describe how to set up/down step-size in open loop power control for WiBro reverse link. Since open loop power control does not use feedback information, it is difficult to efficiently use wireless resource with accurate power control. We also provide a method of estimating levels of noise and interference. With numerical investigation, asymmetric up/down power-control step-size is shown to be promising to achieve high sector throughput as well as low error rate.

Conventional decode-and-forward (DF) relaying with multiple relays can increase the reliability by creating a virtual antenna array, but induces the capacity loss. We introduce a DF relaying with distributed beamforming (DBF) which has better reliability than conventional DF relaying as well as increases the capacity. Under the power constraints of each relay, not the total sum power of all relays, we find the optimal DBF weights, for each relay, which maximize the received signal-to-noise ratio (SNR) at the destination. We derive an approximated probability density function (PDF) of received SNR and analyze the outage probability in Rayleigh fading channels. Numerical results show that derived probability is very well matched with the simulation results.

Greedy transmission scheduling achieves great capacity by maximally exploiting independent time-varying channels across different mobile users. The improvement in capacity, however, depends on the degree of completeness of the channel quality information (CQI) fed back from the receiver to the transmitter. To be motivated by an insight that too many CQI feedbacks may rather impair the capacity gain, due to causing congestion in feedback link, this letter proposes a quality-based CQI reporting (QBR) scheme where the CQIs are fed back to the transmitter only for receivers whose signal quality is above a predefined threshold. The capacity is provided in terms of the threshold and feedback-error rate. The results show that QBR achieves outstanding performance when the feedback error is present. In addition, it quickly approaches an unimpaired ideal capacity, as the number of users increases if the error is not assumed

In this paper, we propose a multiple-input multiple-output (MIMO) mobile-to-mobile channel simulation model derived from a non-realizable reference model presented in Part I of our paper. The underlying reference model is based on the geometrical two-ring scattering model, where both the transmitter and the receiver are moving. A closed-form solution is provided for the three dimensional (3-D) space-time cross-correlation function (CCF) of the simulation model. An important result is that this CCF is ergodic. Also, our results show that this 3-D function can be expressed as a product of two 2-D space-time CCF, called the transmit and the receive CCE. It is shown that the parameters of the simulation model can be determined for any given space-time CCF describing the reference model. In case of isotropic scattering, we present a closed-form solution of the model parameters and illustrate some numerical results for the transmit and receive CCF. Finally, simulation results show an excellent correspondence between the statistical and time average of the MIMO channel capacity. This supports the hypothesis that the MIMO capacity is ergodic with respect to the mean.

In this paper, we propose a muiltiple-input multiple-output (MIMO) channel model for mobile-to-mobile commmunications. This so-called MIMO mobile-to-mobile channel model is derived from the geometrical two-ring scattering model under the assumption that both the transmitter and the receiver are moving. In Part I of our paper. we focus on the reference model. which is based on the assumption that the transmitter and the receiver are surrounded by an infinite number of local scatterers. From a wave model, the complex channel gains are derived and their statistical properties are studied. General analytical solutions are provided for the three-dimenisional (3-D) space-time cross-correlation function (CCF). We show that this 3-D function cani be expressed as the product of two 2-D space-time CCFs, which are introduced as the transmit arid receive CCF. Especially for the latter CCFs, closed-form expressions and numerical results are presented in case of isotropic scattering. The procedure presented in our paper provides an important framework for designers of future mobile-to-mobile communication systems to verify new transmission concepts under certain propagation conditions.

This paper proposes a power cost of mobility that is needed to compensate for fast fading. By the power cost of mobility we mean the additional SINR (signal-to-interference-plus-noise ratio) that is needed to meet the signal quality because the user is mobile. That is, the power cost of mobility in this paper is defined as the increment in power-control target SINR due to fast fading. We consider closed-loop power control (CLPC) based on SNR (signal-to-noise ratio) instead of SINR because it is difficult to analyze statistically power-controlled interference. The channel is modeled as flat Rayleigh fading. The probability density function (pdf) of the received SNR is derived in terms of the power control updating rate, maximum SNR, and Doppler frequency of the fading channel. In cellular systems with quadrature phase shift keying (QPSK) modulation, we study the power cost with various power control updating rates and Doppler frequencies of the fading channel.

In this paper, it is shown that, in DS/CDMA mobile systems, halving or doubling the spreading factor (HSF or DSF) when retransmission is requested possibly improves the throughput. Given transmit power, DSF essentially decreases probability of packet error (PPE) by increasing the signal energy per information bit. It, however, doubles the time duration needed for transmitting the original packet. On the other hand, HSF increases PPE. It, however halves the time duration required to carry the original packet. Thus, the efficiency of HSF in DSF as a retransmission strategy depends on the amount of increased or reduced PPF after HSF or DSF is selected. With achieving given residual error probability (REP) in CDMA systems, the effective throughput is evaluated in this paper to find conditions with which HSF or DSF achieves better performance than using the original one. Analytic results show that HSF or DSF performs better when relatively small or big changes in their PPE's are present, respectively.

The mobile transmitter power control algorithms that need to exchange the tract information on link gains, interference levels, or signal-to-interference ratio (SIR) between transmitters and receivers have been proved to converge to a unique fixed power allocation. However, such exact exchange requires an excessive bandwidth for signalling traffic. In practical systems, only 1 bit is sent back to each transmitter. The 0-1 binary feedback is used by the transmitter either to increase or to decrease the power level by a predetermined amount. In this study, we prove a convergence property of the binary feedback power control algorithm. Since the power level of each transmitter is changed by a fixed amount at every iteration, we cannot claim that the power converges to a fixed point. Instead, we show that the received SIR of each user falls within a certain specific range that is determined by an SIR target and a power control step-size.

Blocking handoff calls which results in the forced termination of ongoing call is significantly undesirable than blocking new call attempts. Thus, call admission policies that give a priority to handoff calls have been intensively studied. For reducing the probability of forced termination, priority has been given to handoff calls over newly originating calls by reserving a number of channels exclusively for handoffs, which is known as the guard channels. We define a new method of giving a priority to handoff calls by using different thresholds when admitting new calls and handoff calls respectively. This method is especially useful in code division multiple access (CDMA) systems, where the capacity is limited by the total level of interference from the connected mobiles, call attempts are blocked when the interference level reaches a predetermined threshold above the background noise level. We define the interference-based prioritized call admission control (IPCAC) and consider various prioritised call admission strategies for practical CDMA systems where receiver processors also limit the call-blocking performance: call admission only with GCP, IPCAC with and without GCP, respectively. The performances are numerically evaluated and compared for various system parameters. Conclusions are drawn regarding the usefulness of prioritizing strategies under various traffic conditions that are characterized by the traffic load and the mobile speed.

In code division multiple access (CDMA) mobile networks, transmitted power is controlled to provide each user an acceptable connection by limiting the interference seen by other users. Previous work has focused on finding a power assignment that maximizes the minimum carrier-to-interference ratio where the transmission rate of each user is known and fixed. In future mobile networks, however, fluctuations in mobiles' transmission rate should be considered in designing power control algorithms. In this work, we present an algorithm for controlling mobiles' transmitter power levels while explicitly handling their time-varying transmission rates. During the whole power control process, the required signal quality is always maintained. The traffic-carrying performance of the algorithm is evaluated by simulation where different types of users are sending burst data.