Location-Based Services (LBSs) using wireless communication systems have witnessed a dramatic increase in both demand and applicability. In particular, there is a need for high-accuracy position estimation in dense indoor environments, while sustaining data communication services. In this paper, analytical expressions are formulated to characterize the trade-off between the position estimation accuracy and the latency/throughput performance in a multi-user IEEE 802.11az scenario. Furthermore, optimization frameworks are developed using which the proposed enhancements can tune the degree of trade-off, in terms of the number of preamble symbol repetitions. The impact of the desired position accuracy, Signal-to-Noise Ratio (SNR), bandwidth, and user-grouping strategies are evaluated as well.

A channel time variation suppression scheme based on beamforming is proposed for high-mobility orthogonal frequency division multiplexing (OFDM) downlink transmissions. The residual channel time variation after Doppler shift compensation by finite resolution receive beamforming can be measured by the Doppler spread. The interchannel interference (ICI) due to the time-varying channel is then analyzed and the relation between the signal-to-interference ratio (SIR) and Doppler spread is given. Based on the derived Doppler spread and ICI, a beamforming network optimization scheme is proposed to reduce the channel time variation. A closed-form solution is first obtained to minimize the average ICI, which exploits the structure of a tridiagonal Toeplitz matrix. Next, an optimization problem is formulated to minimize the maximum Doppler spread to further verify the impact of average ICI on channel time variation. The sequential parametric convex approximation (SPCA) algorithm is exploited to solve the non-convex min-max problem. Numerical results verify the theoretical analysis.

Wide area networks for surveying applications, such as seismic acquisition, have been witnessing a significant increase in node density and area, where large amounts of data have to be transferred in real-time. While cables can meet these requirements, they account for a majority of the equipment weight, maintenance, and labor costs. A novel wireless network architecture, compliant with the IEEE 802.11ad standard, is proposed for establishing scalable, energy-efficient, and gigabit-rate backhaul across very large areas. Statistical path-loss and line-of-sight models are derived using real-world topographic data in well-known seismic regions. Additionally, a cross-layer analytical model is derived for 802.11 systems that can characterize the overall latency and power consumption under the impact of co-channel interference. On the basis of these models, a Frame Aggregation Power-Saving Backhaul (FA-PSB) scheme is proposed for near-optimal power conservation under a latency constraint, through a duty-cycled approach. A performance evaluation with respect to the survey size and data generation rate reveals that the proposed architecture and the FA-PSB scheme can support real-time acquisition in large-scale high-density scenarios while operating with minimal power consumption, thereby enhancing the lifetime of wireless seismic surveys. The FA-PSB scheme can be applied to cellular backhaul and sensor networks as well.

Modern seismic surveys can obtain subsurface images of superior quality and depth, albeit requiring wireless acquisition systems to keep up with higher data rate requirements. Data communication protocols have been studied primarily for links between the geophones and the gateway nodes, leaving a dearth of analysis for the communication links between the gateway nodes and the sink node. In this paper, a novel wireless geophone network architecture based on the IEEE 802.11ad standard is proposed with the objective of providing gigabit rates in order to support real-time seismic acquisition. A performance analysis reveals that the latency and power consumption are dependent on the ratio of the data generation rate to the data transfer rate. An additional Power-Saving Geophone Relay (PSGR) scheme is described, which exploits idle periods of operation to conserve power at the cost of an increased latency. The trade-off between the latency and power consumption under the PSGR scheme is evaluated for a variety of scenarios in seismic acquisition.

The integrated radar and communications system (IRCS) is promising for Unmanned Air Vehicles (UAVs). However, due to fast varying channels caused by high mobility, it is a tremendous challenge for the fusion center to collect detection information within the delay threshold. Based on only path loss of the channel, this paper performs power allocation to minimize the total transmit power while meeting the detection performance for radar and guaranteeing the latency violation probability (LVP) for communication. Using effective capacity theory, the latency constraint is expressed with introduced latency exponents. The resource allocation problem is non-convex and formulated to a convex one, which can be solved with a global optimum. Simulation results demonstrate the effectiveness of the proposed algorithm from the perspectives of the total transmit power and the latency of the communication links.

Modern geophysics methods for oil and gas exploration are able to generate subsurface images of superior quality and depth, albeit making real-time data acquisition a more challenging task. While current literature addresses data transfer issues primarily between the geophones and the gateway nodes, a communication scheme for the transfer of data from the gateway nodes to the sink largely remains unsolved. A novel wireless geophone network architecture for seismic data acquisition is described, with the objective of eliminating cable-based systems and providing Gigabit rates in order to support real-time acquisition. A performance analysis is conducted for various mesh networks employing IEEE 802.11ac, IEEE 802.11ad, and free space optical communication, from the geophysics perspective. Our findings suggest that the bottleneck links can be shifted from the top to the bottom of existing architectures, and a scalable approach requiring minimal number of gateway devices can be designed for high-density seismic surveys.

Seismic surveys are conducted by oil exploration companies to keep up with the global demand for oil and gas. Although seismic cables offer fast and reliable data transfer, they account for a majority of the equipment weight, logistics, and labor costs. A novel wireless geophone network architecture, compliant with the IEEE 802.11af standard, is described. Operation in television white spaces can achieve long transmission ranges, allowing for scalable coverage of large seismic survey areas. Two methods for data collection are proposed: a Geophone-Polling (GP) scheme and an Adaptive Geophone Time Division Multiple Access Scheduling (AGTS) scheme. The two schemes are analyzed and evaluated in terms of the total time taken for data acquisition and the average power consumption, in comparison to the default IEEE 802.11 channel access schemes. The problem of hexagonal clustering for orthogonal deployment of geophones is also tackled, and the impact of co-channel interference is considered. The proposed schemes not only reduce data acquisition time, but also the average power consumption of the geophones, thereby improving the lifetime of wireless seismic surveys.

Full-duplex (FD) D2D communications have been recently applied in cooperative caching systems with advanced self-cancellation technologies. A FD mode relay can receive a content item from a Content Provider (CP), and forward it to a Content Requester (CR) simultaneously on the same band. However, FD mode relays and CPs are generally selfish, thus an effective incentive mechanism to encourage their mutual cooperation is important. Complicating the matter, there exist information asymmetries between the CP and relay. For example, a relay's channel state information is personal character information, which is called as hidden information. Also, the transmission power of relay is personal action information, which is called as hidden action. The asymmetric information problem may lead to deceptive behavior during cooperation. Therefore, an adverse selection and moral hazard model based incentive mechanism is proposed, which solves the hidden action and hidden information problems jointly. The capacity of this two-hop relay transmission serves as metric, and an effective power allocation method is designed based on the incentive contract.

Traditional seismic data acquisition systems rely on telemetry cables to conduct oil, gas, and mineral exploration. Although cabled systems provide reliable seismic data transfer, their deployment and maintenance costs are increasing substantially as surveys become larger in scale and densely populated. A novel wireless geophone network architecture is proposed and described in this paper, which makes use of the IEEE 802.11af standard. It operates in the TV White Space, which offers a significantly higher transmission range. A data collection scheme is also proposed and its performance in comparison to the default 802.11 schemes is evaluated on NS-3. The proposed scheme is standards compliant; no changes to the IEEE 802.11af standard are required. The problem of hexagonal clustering for orthogonal deployment of geophones is also considered, and the impact of co-channel interference is analyzed. Furthermore, energy-aware algorithms are analyzed to extend the battery life of the geophones. The proposed scheme outperforms the default standard in terms of both throughput and power consumption, and provides a realistic solution for deploying large-scale wireless geophone networks.

Traditional seismic data acquisition systems used for surveying during the exploration of oil and gas rely on cables between geophones and data collection center. Despite the fact that cable-based systems provide reliable seismic data transfer, their deployment and maintenance costs increase substantially as the survey area increases in scale. This paper investigates the aggregate data throughput and transmission time from wireless geophones to gateway node in a wireless geophone network architecture based on IEEE802.11af standard. The analytical expressions of throughput and transmission time are derived using Markov chain models. Two Markov models are considered for this purpose: one for modeling carrier sense multiple access method with collision avoidance (CSMA/CA) behavior and the other for representing a buffer in a wireless geophone. Furthermore, the physical layer path-loss models are taken into account.

Wireless systems for seismic data acquisition offer several advantages over cable-based systems by reducing human impact on the environment and the costs associated with deployment, maintenance, and logistics. Millimeter-wave communication offers the requisite data rates to rapidly transfer large amounts of seismic data. A novel wireless geophone network architecture is described, based on the IEEE 802.11ad standard. A data collection scheme is also presented, resulting in a reduction of the total number of wireless gateways required in large-scale seismic surveys. Beamforming techniques are used to reduce co-channel interference, as per the geophone topology. Techniques for power conservation and propagation modelling are investigated. A performance evaluation in terms of the channel access scheme, throughput, and power consumption, is conducted on ns-3. The proposed wireless acquisition system provides a feasible and standards-compliant approach for deploying large-scale wireless geophone networks.

Non-stationary mobile-to-mobile (M2M) channel modeling has gained strong momentum as it is vital for developing M2M communications technology. Traditional geometry-based channel models (GSCMs) for M2M communications usually assume fixed velocity and moving direction, which differs from the realistic M2M scenarios and also makes it difficult to incorporate non-stationarity of channel into the regular-shaped GSCMs. In this paper, a mobility model-based method is proposed to incorporate non-stationarity into M2M channel modeling by introducing dynamic velocities and trajectories. A revised Gauss-Markov mobility model is first presented together with the cluster-based two-ring M2M reference model. The mobility model uses tuning parameters to adjust the degree of mobility randomness and covers different M2M mobility trajectories. Then, a closed-form time-variant time-frequency correlation function and the Doppler power spectrum are derived from the model. Based on the numerical analysis, it is found that for a regular-shaped GSCM with a fixed M2M scattering environment, the motion does not introduce non-stationarity, however, the dynamic motion (i.e., the changes of velocity and moving direction) leads to non-stationarity, which is reflected by the time-variant time correlation function and Doppler spectrum. Different propagation modes, cluster number, and intra-cluster nonisotropic scattering also have major impacts on channel non-stationarity. Moreover, the randomness of the mobility model is found to significantly increase the degree of channel non-stationarity. These conclusions are useful for M2M non-stationary channel simulation and communication system evaluation.

This paper proposes a novel joint pilot assignment (JPA) approach aiming to eliminate pilot contamination in massive multiple-input multiple- output (MIMO) systems. The JPA approach jointly assigns pilots in both the time domain and spatial domain. With JPA, the multi-cell cellular massive MIMO network is divided into four cell groups. Pilot phases of different groups are designed to be successive in time domain, which means that users in different groups send pilots alternately in time domain. During the pilot phase of each group, a greedy spatial domain pilot assignment (SDPA) is introduced with the criterion of maximizing the minimal user signal-to-interference ratio (SIR). This paper shows that the JPA approach significantly eliminates pilot contamination from inter-groups when a finite but large number of base-station (BS) antennas is used, or even completely removed as the number of BS antennas becomes unbounded. Since the minimal uplink user SIR is increased, i.e., the intra-group pilot contamination is also alleviated. Numerical results verify the theoretical analysis.

This work studies secrecy enhancement for socially enabled communications in cellular device-to-device (D2D) underlay through resource allocation. By analyzing the impact of social characteristics of those involved D2D users (DUs), proper selection of transmitters and friendly jammer nodes with appropriate power and spectrum allocation can facilitate secrecy transmission. First, we select D2D transmitter by characterizing the link to guarantee the desired success rate without downgrading the service requirement for impacted cellular users (CUs). Furthermore, jammers' trustiness based on their own social interaction is considered for secrecy enhancement. Numerical results verify the performance of our proposed scheme.

This paper analyzes the effect of distributed time-reversal (DTR) transmission scheme on the signal-to-noise ratio (SNR) at its intended and unintended receivers. By focusing the temporal and spatial signal energy on the intended receiver, DTR can effectively maintain a satisfactory SNR level while lowering received signal level at passive eavesdroppers or unintended co-channel users. The DTR performance is analyzed in terms of a SNR gap between the desired and unintended receivers. The SNR gain of DTR is also analyzed over traditional distributed direct transmission and several cooperative beamforming transmission schemes without time-reversal. Numerical results demonstrate the performance improvement of the time-reversal transmission and the validity of our analytical results.

This paper investigates the problem of resource and power allocation in device-to-device (D2D) underlays given a specific secrecy rate constraint. The objective is to optimize the pairing of D2D links with cellular user equipment (CUE) uplink channel resources, and to allocate their respective powers to combat against eavesdroppers for secrecy rate improvement. The proposed method first determines a set of candidate D2D links with the required signal-to-interference-plus- noise ratio level for each CUE to narrow the number of combinatorial sharing options. Afterwards, an optimization problem is formulated for maximizing the overall secrecy rate under user power constraints and minimum required secrecy rates. Finally, numerical results demonstrate the resulting performance.

LTE/LTE-A networks have been successfully providing advanced broadband services to millions of users worldwide. Lately, it has been suggested to use LTE networks for mission-critical applications like public safety, smart grid and military communications. We have previously shown that LTE networks are vulnerable to Denial-of-Service (DOS) and loss of service attacks from smart jammers. In this paper, we extend our previous work on resilience of LTE networks to wideband multipath fading channel, SINR estimation in frequency domain and computation of utilities based on observable parameters under the framework of single-shot and repeated games with asymmetric information. In a single-shot game formulation, network utility is severely compromised at its solutions, i.e. at the Nash Equilibria (NE). We propose evolved repeated-game strategy algorithms to combat smart jamming attacks that can be implemented in existing deployments using current technology.

In coordinated multi-point (CoMP) transmission systems, coordinated base stations (BSs) are geographically separated and have their own oscillators, thereby causing multiple carrier frequency offsets (CFOs) at the receiver. Therefore, perfect synchronization cannot be obtained at the mobile station (MS), resulting in severe interference. To resolve this problem, this study proposes a novel transceiver structure with improved robustness toward interference. With the knowledge of CFO and channel frequency response, a closed-form solution is derived for the sub-optimal CFO compensation value to minimize the approximated upper bound of the inter-carrier interference (ICI) plus noise power for environments with large-scale fading. The results reveal that the sub-optimal CFO compensation value is a function of both the degree of large-scale fading and the value of CFOs. Simulation results demonstrate that the proposed method significantly outperforms the existing structures and exhibits improved performance in terms of bit error rate.

Commercial LTE networks are being studied for mission-critical applications, such as public safety and smart grid communications. In this paper, LTE networks are shown vulnerable to Denial-of-Service (DOS) and loss of service attacks from smart jammers, who may employ simple narrowband jamming techniques to attack without any need to hack the network or its users. We modeled the utilities of jamming and anti-jamming actions played by the jammer and the network under the framework of single-shot and repeated Bayesian games. In a single-shot game formulation the only Nash Equilibria (NE) are pure strategy equilibria at which network utility is severely compromised. We propose a repeated-game learning and strategy algorithm for the network that outperforms single-shot games by a significant margin. Furthermore, all of our proposed actions and algorithms can be implemented with current technology.

A wireless polarized-channel simulator is described that can generate a variety of polarized-channel impulse responses. The simulator is useful in the broad research area of polarization-utilizing wireless communication systems. The simulator relies on a geometrically based statistical model (GBSM) for polarized wide-band channels, and consists of three-dimensional (3-D) concentric scattering cylinders about the mobile station. It can be used to model a polarized wide-band cellular down-link channel. To the best of our knowledge, our polarized-channel simulator is the first such simulation model that can generate the time-variant channel impulse response of polarized wide-band wireless fading channels. The simulator utilizes previously reported geometrical theory and reference models for cross-polarization discrimination (XPD), and shows excellent agreement with the reference models, while considering only a finite number of scatterers both for good accuracy and manageable computational complexity.

Two receiver architectures are presented for equalization of multi-h continuous phase modulation (CPM). In the first approach, the receiver front end is a matched-filter bank, which is derived from Laurent decomposition of the signal. A circulant-matrix model derived for the samples of the matched filter is used to perform the equalization in frequency domain. The second technique employs a receiver with a simple front end consisting of a low-pass filter and a fractional sampler. We also develop a circulant matrix model for the latter approach, which relates the Laurent pseudo-symbols to each polyphase component at the output of the sampler. A linear frequency-domain equalizer (FDE) is also proposed using this model. In addition to providing the details of these approaches, the paper proposes several simplifications applicable to each of the two cases, and provides a detailed discussion on the performance/complexity trade-off. Bit-error rate (BER) results are presented for the IRIG-106 aeronautical telemetry dual-h CPM waveform.

A cellular down-link polarization division multiple access (PDMA) scheme with collaborative transmitter-receiver-polarization adjustment and polarization filtering detection is proposed for polarized wide-band non-line-of-sight (NLoS) wireless fading channels. The fundamental novelty of the proposed scheme is that it can adjust transmit polarization to yield more desirable per-subcarrier complex cross-polarization discrimination (XPD) observed at the receivers. This is a significant difference between the proposed scheme and conventional multiple-input multiple-output (MIMO) systems. The capacity analysis of the proposed PDMA scheme is provided, and the feasibility and satisfactory performance of the scheme are demonstrated even when serious time-variant channel depolarization and polarization mismatch between receivers occurs. The proposed cellular down-link PDMA scheme uses synchronous orthogonal frequency division multiple access (OFDMA) with an equally spaced pilot symbol allocation and a channel estimator. Excellent symbol error rate (SER)/effective signal-to-interference plus noise ratio (SINR) performance is shown despite the presence of substantial channel depolarization. The scheme can be used to extend the capacity of any cellular system that uses uni-polarized antennas and can be extended and applied to MIMO arrays as well.

In this paper, we study the cross layer design and optimization for delay quality-of-service (QoS) provisioning in spectrum sharing femtocell networks. Our goal is to find the optimal resource allocation policy to maximize the throughput for each femtocell user, addressing the co-channel interference problem in the physical layer and the individual statistical delay-QoS guarantee problem from the upper layers. The statistical delay-QoS requirement is characterized by the QoS exponent. By integrating the concept of effective capacity, the cross-layer optimization problem is formulated as an effective capacity maximization game. With partial dual decomposition, this game is solved through a hierarchical structure. Specifically, we derive the optimal power allocation policy for femtocell users and design a distributed algorithm to obtain the Nash Equilibrium (N.E.). Numerical results show that the proposed policy can efficiently improve the performance of the networks.

Frequency-domain equalization (FDE) is a low-complexity approach to remove the effects of intersymbol interference (ISI) introduced by propagation over a frequency-selective channel. In this paper, we present a novel receiver architecture for frequency-domain equalization of multi-h continuous phase modulation (CPM). The receiver front-end is a matched-filter bank, which is derived from a Laurent decomposition of the signal. A circulant-matrix model obtained for the samples of the matched filter is used to perform the equalization in frequency domain. It is shown that receiver complexity can be reduced by allowing a slight degradation in performance. The reduction in the complexity of the equalizer is proposed by dropping the FDE branches corresponding to low-energy Laurent pulses. It is observed that the loss in performance is acceptable even when a few significant branches are considered. Simulation results are presented for the IRIG-106 aeronautical telemetry dual-h CPM waveform.

This paper proposes a dynamic bound restriction iterative algorithm (DBRIA) framework, which can make iterative algorithms converge quickly. We apply this framework to realize computationally efficient iteration-based suboptimal bit and power allocation in OFDM systems. The implementation methods for three classes of suboptimal allocation algorithms are analyzed; margin-based, water-filling-based, and Lagrange-multiplier-based. We extend the water-filling-based power allocation algorithm to implement the bit allocation as well. Additional techniques for further reducing the computational complexity for all three allocation methods are also discussed. Simulation results show that both the maximum and the average computational complexity of all three allocation algorithms are reduced dramatically by applying the DBRIA and the additional techniques. For the water-filling-based algorithm, the allocation performance is also improved.

Conventional uni-polarized multiple input multiple output (MIMO) antenna systems offer the advantages of higher data rate and higher reliability through the use of spatial multiplexing and space-time coding, respectively. However, the cost and space constraints have led to the use of dual-polarized MIMO antenna systems where two spatially separated uni-polarized antennas are replaced by a single antenna element employing orthogonal polarizations, thereby exploiting polarization diversity. The advantages of dual polarized antennas can be further exploited by the use of precoding at the transmitter which leads to reduced complexity at the receiver for downlink communications, when compared to the conventional multi-user detectors. In this paper, we propose a singular value decomposition based precoding-aided dual-polarized MIMO system and compare its performance with the conventional minimum mean square error (MMSE) based approach for mitigating co-channel interference in a multi-cell environment consisting of flat Rayleigh fading channels. Our performance results reveal that the pre-coding aided dual-polarized MIMO system outperforms the conventional MMSE detection scheme and offers appreciable gain in symbol energy-to-noise ratio performance.

This paper considers the construction of a symbol block to generate a cyclic multi-h continuous phase modulated (CPM) signal so as to permit frequency domain equalization (FDE) at the receiver. Like single-h CPM, the memory inherent in a multi-h CPM waveform requires an intra-fix in each transmitted block. We propose a novel procedure that determines the intra-fix symbols, such that the intra-fix length is minimized. The constraints on the required intra-fix symbols are shown to form a set of Linear Diophantine Equations (LDEs). The proposed procedure is applied to a dual-h CPM scheme.

General multi-branch multi-hop (MBMH) cooperative diversity systems with decode-and-forward (DF) relays are investigated on non-identical Nakagami-m fading channels in the presence of an arbitrary number of non-identical co-channel interferers. This paper presents exact closed-forms for the probability density function of the signal-to-interference-plus-noise ratio and the outage probability of a DF MBMH cooperative relaying system. The results show that the performance of the DF MBMH cooperative relaying system is more vulnerable when co-channel interferers are closer to the destination than when they are closer to the relays. Our analytical results are verified by Monte Carlo simulations.

This paper considers the problem of constructing a symbol block to generate a cyclic multi-h continuous phase modulated (CPM) signal so as to permit frequency domain equalization (FDE) at the receiver. Like single-h CPM, the memory inherent in a multi-h CPM waveform requires the use of an additional segment, called an intra-fix, in each transmitted block. The intra-fix forces the transmitter state machine to regress to the state it had at the start of the block. The constraints on the symbols of the intra-fix, which ensure above condition, are shown to be a set of Linear Diophantine Equations (LDEs). Three different methods are proposed for finding the symbols of the intra-fix, such that the length of the intra-fix is minimized. The last two methods connect the problem of intra-fix insertion to the problem of trellis termination of the tilted phase. This connection enables us to state and justify that existing bounds established on the length of the terminating sequence are effective for the length of the intra-fix. We observe that multi-h CPM schemes typically require a shorter intra-fix, as compared to single-h CPM schemes having similar modulation parameters. We apply the proposed procedure to a dual-h CPM scheme.

Efficient design of spectrum-sensing and power control plays a key role in maximizing the throughput of a cognitive radio (CR) network while protecting the PUs from undue interference. In this paper, we consider the problem of joint spectrum-sensing-duration design and power control in a point-to-point CR link. The objective of the proposed solution is to maximize the CR achievable throughput while keeping the CR interference to the primary user (PU) at or below a preset interference threshold. The joint spectrum-sensing design and power control is a non-convex optimization problem, hence, obtaining the optimal solution may not be always feasible. In this paper, we formulate the joint sensing-duration design and power control problem as a two-stage stochastic program with recourse. Afterward, we derive the formulas for the achievable throughput as a function of the sensing duration. Moreover, we investigate the effect of different levels of knowledge of the interference channel state information (CSI) on the achievable throughput and the optimal sensing duration.

The issues of frequency offset and channel estimation are considered for the downlink of coordinated multiple-input multiple-output orthogonal frequency-division multiplexing systems. Multiple carrier frequency offsets exist in this coordinated system. Without implementing an appropriate compensation for these offsets, both inter-carrier and inter-cell interference will degrade the system performance. Here, we adopt a parallel interference cancelation strategy to iteratively mitigate inter-cell interference, and propose a frequency offset estimator, approximated by a Hadamard product and a Taylor series expansion, to eliminate the inter-carrier interference. Our scheme is significantly less complex than existing methods. Furthermore, the proposed channel estimator is robust to frequency offsets and performs comparably well to these conventional approaches.

This paper analyzes the outage probability of multi-branch dual-hop decode-and-forward (DF) cooperative relaying systems over non-identical Nakagami/Nakagami fading channels. The paper derives an exact closed-form expression for the outage probability with maximum ratio combining considering both the effect of co-channel interference (CCI) and addictive white Gaussian noise. The results of this paper show that a DF cooperative relaying system is more vulnerable to noise than interference for low and moderate SINR, whereas it is more susceptible to interference than noise for high SINR and high diversity order. Moreover, this paper shows that the robustness of the destination against CCI is more important than that of the relay. The results of this paper are verified by Monte Carlo simulations.

General multi-branch multi-hop (MBMH) cooperative diversity systems with selection decode-and-forward (DF) relays are investigated on non-identical shadowed Nakagami-m fading channels in the presence of an arbitrary number of non-identical co-channel interferers. This paper presents closed-form expressions for the outage probability, the average symbol error probability, and the probability density function of signal-to-interference-plus-noise ratio of the selection DF MBMH cooperative relaying system. The results of the paper show that outage and error performance improvements against shadowing stem from the number of branches rather than the number of hops for a fixed number of relays. The results also show that the performance of the selection DF MBMH cooperative relaying system is more vulnerable when co-channel interferers are closer to the destination than when they are closer to the relays. This analysis is verified by Monte Carlo simulations.

This paper proposes a new optimal bit and power direct allocation algorithm. Based on the analysis of the regularity of the Greedy allocation result, we propose and prove a necessary and sufficient condition for the Greedy allocation result. According to this condition, a bit and power allocation algorithm aiming to allocate the total bits or total power at a time to all subchannels is proposed. The impact of SNR Gap on the allocation result and the technique to eliminate its impact are analyzed. Though iterations are needed to obtain the ideal allocation result, the computational complexity is lower than that of existing optimal algorithms in the literature, even lower than that of some suboptimal algorithms.

This paper addresses the problem of cyclic prefix insertion for multi-h CPM waveforms. Like single-h CPM, the memory inherent in a multi-h CPM waveform, and its continuous nature, requires the use of an intra-fix in each transmitted block. We identify the structure of the block, the constraints on its length, and the symbols of the intra-fix. A procedure is proposed for finding the symbols of the intra-fix using the tilted phase transformation. The procedure ensures that the overhead due to the intra-fix is minimized. Bounds on the intra-fix length are also presented in terms of parameters of the modulation scheme. The proposed procedure is applied on a dual-h CPM scheme for illustration of analytical results.

We consider the issues of frequency offset and channel estimation in downlink coordinated multiple-input multiple-output orthogonal frequency-division multiplexing systems. Multiple carrier frequency offsets exist in this coordinated system. Without implementing an appropriate compensation for these offsets, both inter-carrier and inter-cell interference will degrade system performance. In response, we adopt parallel interference cancelation to iteratively mitigate inter-cell interference, and propose a frequency offset estimator, approximated by Hadamard product and Taylor expansion, to eliminate the inter-carrier interference. Our scheme is significantly less computational complex than the existing methods. Furthermore, the proposed channel estimator is robust to frequency offsets and performs comparably to conventional approaches.

This paper presents a method for terminating the phase trellis in Multi-h Continuous Phase modulation (CPM). It is shown that tilted phase trellis for a Multi-h CPM signal is periodic and enables the representation of the modulator as the cascade of a periodic recursive continuous phase encoder (CPE) and a phase modulator (PM). We then pose the problem of finding the number of symbols that will terminate the tilted phase trellis, and establish a connection of its solution to the Diophantine Frobenius Problem (FP). Results are derived for the existence of a terminating sequence (TS), and bounds are established on its length in terms of the modulation parameters.

This paper presents a method for terminating the phase trellis in multi-h continuous phase modulation (CPM). It is shown that tilted phase trellis for multi-h CPM signals is periodic and enables the representation of the multi-h CPM modulator as a cascade of a periodic recursive continuous phase encoder (CPE) and a phase modulator (PM). We then pose the problem of finding the minimum number of symbols that will terminate the phase trellis in a known state of the modulator and establish a connection of its solution to the Diophantine Frobenius Problem (FP). Analytical results are established for the existence of a terminating sequence and upper and lower bounds are derived on its length for arbitrary modulation parameters. We show that the trellis terminating symbols and their quantity depends upon the initial state of the encoder, the set of modulation indices, the CPE memory order, and the number of bits per modulated symbol. It is shown that required overhead for trellis termination can be significant for schemes with integer modulation indices.

Multi-channel, multi-interface ad hoc wireless networks can obtain substantial capacity improvements by mitigating co-channel interference. Channel assignment and routing algorithms that relieve co-channel interference and balance traffic loads are critical for obtaining these large capacity increases. However, with a limited number of channels and interfaces, this approach cannot avoid traffic overload as the network traffic increases. This paper proposes a novel scheme of multi-channel/interface network coding that is based on the combination of a new concept of coded-overhearing and coding-aware channel assignment. The proposed algorithms overcome the radio coverage limitations present in conventional network coding schemes, and exhibit improved flexibility in terms of aggregate throughput when there are an insufficient number of interfaces and a outage of network coding opportunities. Our scheme attains significant improvement in the aggregate throughput as compared to a no network coding scheme.

In this paper, a channel precoding technique is proposed for M-ary continuous phase modulation (CPM) for multipath downlink channels. The proposed pre-equalizer, based on the approximation of CPM signals by complex exponential functions, applies modulo-arithmetic operations to ensure the stability as in Tomlinson-Harashima method. Spectrally efficient precoded signals are obtained with small envelope variations by employing a transmit antenna selection technique. Because the equalization functions are transferred to the base station, the complexity in the mobile terminals is reduced significantly. The simulation results depict the power spectral density of the transmitted signals and the bit-error rate. An upper bound on the error performance is computed and the relation between the number of transmit antennas and the spectral efficiency is derived.

A new three-dimensional (3-D) geometry-based reference model for cross-polarization discrimination (XPD) is proposed for narrow-band vehicle-to-vehicle (V2V) channels. The model is based on the superposition of polarization components on conservation-of-polarization planes (CoP-planes). This novel approach is used to derive the XPD at each distance. To the best of our knowledge this is the first purely theoretical geometry-based XPD reference model of V2V channels. Using our reference model, we obtain a relationship between XPD and channel modeling factors such as the distance between the transmitter (Tx) and the receiver (Rx), the azimuth/elevation angles of arrival and departure (A/E-AoA and A/E-AoD), multipath delays, and the distribution of scatterers. The proposed XPD reference model for V2V channels is based on and extended from our previous XPD reference model for fixed-to-fixed/mobile(F2F/F2M) channels. Our analytical XPD model reveals valuable XPD properties that expose the potential of utilizing polarization diversity in V2V communication systems.

This paper investigates the problem of downlink power allocation in a Cognitive Radio (CR) network that operates by opportunistically utilizing vacant licensed Primary User (PU)spectrum, where it is assumed the PU employs an OFDMA scheme. We first analyze the interference to the PU caused by the CR network due to imperfect spectrum sensing and out-of-band (OOB) emissions from CR subcarrier side-lobes. The power allocation algorithm aims to maximize the CR network capacity under interference constraints, while considering the effect of spectrum sensing errors such as false alarm and misdetection probabilities. The power allocation solution for a single-user CR network is the waterfilling criteria with a variable water level in different subcarriers. For a multiple-user CR network, we employ a heuristic algorithm to solve the power allocation problem, with a significantly reduced computational complexity as compared to the optimal solution.

This paper analyzes the outage probability for a decode-and-forward (DF) cooperative diversity system with selective combining, for the case of a log-normal Nakagami faded desired signal and log-normal Rayleigh faded co-channel interferers. The outage probability is compared to that of a dual-receive antenna system also with selective combining. The results of the analysis show that the proposed DF cooperative diversity system can result in a lower outage probability than the corresponding dual-receive antenna system, but only when the relay is located in a particular region of the cell with respect to the mobile station location.

This paper investigates the problem of uplink subcarrier and power allocation in a Cognitive Radio (CR) network that operates opportunistically within vacant licensed Primary Users (PUs)spectrum. The resource allocation algorithm aims to maximize the CR network throughput under PUs interference constraints. In this paper, CR interference introduced into PUs sub-bands is modeled as a composite of two parts; CR Out-of-Band (OOB) emissions and the interference arising as a result of imperfect spectrum sensing. The uplink subcarrier and power allocation is a Mixed Integer Nonlinear Programming (MINLP) problem, for which obtaining the optimal solution is known to be NP-Hard. In this paper, we propose a three steps heuristic solution to the uplink resource allocation problem. We show through simulation that the proposed algorithm exhibits near-optimal performance and comes with a significant reduction in computational complexity when compared to that of obtaining the optimal solution.

A new three-dimensional (3-D) geometry-based reference model for cross-polarization discrimination (XPD) in narrow-band fixed-to-fixed (F-to-F) or fixed-to-mobile (F-to-M) wireless channels is proposed. The proposed model is based on the superposition of polarization components on conservation-of-polarization planes (CoP-planes). This novel approach is used to derive the XPD at each distance without the aid of measurement data or its approximation. To the best of our knowledge this is the first purely theoretical geometry-based XPD reference model. Using our reference model, we obtain a relationship between XPD and channel modeling factors such as the distance between the transmitter and the receiver, the azimuth/elevation angles of arrival and departure (A/E-AoA and A/E-AoD), multipath delays, and the distribution of scatterers. Our analytical XPD model is in close agreement with previously reported results from other authors that are based on empirical measurement data, and it also overcomes the shortcoming of overapproximation/oversimplification of the measurement data.

Abstract This paper analyzes the outage probability for amplify‐and‐forward (AF) and decode‐and‐forward (DF) cooperative diversity systems with selective combining, for the case of a log‐normal Nakagami faded desired signal and log‐normal Rayleigh faded co‐channel interferers. The outage probability is compared to that of a dual‐receive antenna system also with selective combining. The results of this paper show that the proposed cooperative diversity systems can result in a lower outage probability than the corresponding dual‐receive antenna system, but only when the relay is located in a particular region of the cell with respect to the destination mobile station location. Moreover, this paper shows that the AF cooperative diversity system is more robust than the DF cooperative diversity system for the composite channel condition and multiple interferers. Copyright © 2010 John Wiley & Sons, Ltd.

Cognitive radio (CR) has been suggested as a method for promoting more efficient spectrum usage through the principles of spectrum sensing and dynamic spectrum management. The IEEE 802.22 working group in particular is developing a wireless regional-area network (WRAN) standard that will employ unlicensed CR devices operating on a noninterfering basis in the commercial broadcast television (TV) bands. Before such TV-band CR networks can be deployed, the maximum levels of first adjacent and taboo channel interference that a digital television (DTV) receiver can tolerate must be determined. In this context, we will first provide an overview of the IEEE 802.22 WRAN system. Afterwards, we will report on an experimental study that was undertaken to characterize IEEE 802.22 WRAN interference limits into Advanced Television Systems Committee (ATSC) based DTV receivers. Lastly, we will discuss the implications of these WRAN interference limits in terms of the maximum allowable radiated power and out-of-band emission limits that are imposed on WRAN end-user devices.

Multicarrier code division multiple access (MCCDMA) systems using complex-quadratic spreading sequences and cyclic delay diversity (CDD) facilitate frequency or timedomain chip combining to mitigate different types of jamming. In this paper, multiple-input multiple-output (MIMO) channel coefficients, jamming power, and jammer state information (JSI) are jointly estimated to suppress the adverse effects of partial-band noise jamming. We derive weighted least square error (LSE) and linear minimum mean square error (MMSE) channel estimators operating under jamming and investigate the constraints on the cyclic delays. The JSI for the pilot symbols is estimated to assist estimation of the time-varying frequencyselective channel coefficients by updating the noise covariance matrix. We also derive the optimum (sufficient statistics) chipcombining weights for the data symbols that require the JSI; hence, the JSI for the data symbols is iteratively estimated using the decoder output. Simulation results demonstrate that the proposed iterative despreading (includes JSI estimation and chip combining), demapping, and decoding receiver with soft- JSI-assisted channel estimation and chip combining is very robust against partial-band noise jamming.

Sufficient conditions are derived under which$M$-ary partial- and full-response continuous phase modulation (CPM) space–time (ST) codes will attain both full spatial diversity and optimal coding gain. General code construction rules are desirable due to the nonlinearity and inherent memory of the CPM signals which makes manual design or computer search difficult. Using a linear decomposition of CPM signals with tilted phase, we identify a rank criterion for$M$-ary partial- and full-response CPM that specifies the set of allowable modulation indices. We also propose a coding gain design criterion. Optimization of the coding gain for CPM ST codes is shown to depend on the CPM frequency/phase shaping pulse, modulation index, and codewords. The modulation indices and phase shaping functions that improve the coding gain are specified. Finally, optimization of coding gain for ST-CPM and orthogonal ST-CPM codewords is discussed.

A three-dimensional (3-D) geometrical propagation model for wideband multiple-input multiple-output (MIMO) mobile-to-mobile (M-to-M) communications is proposed. Based on the geometrical model, a 3-D parametric reference model for wideband MIMO M-to-M multipath fading channels is developed. From the reference model, the corresponding space-time-frequency correlation function is derived for a 3-D non-isotropic scattering environment. It is shown that the time and frequency dispersion of a wide sense stationary uncorrelated scattering channel cannot be treated independently, contrary to common practice. From the space-time-frequency correlation function, the space-Doppler power spectral density and the power space-delay spectrum are derived and compared with measured data. Finally, a new sum-of-sinusoids based simulation model for wideband MIMO M-to-M Ricean fading channels is proposed. The statistics of the simulation model are verified by simulation. The results show that the simulation model is a good approximation of the reference model.

A three-dimensional reference model for wideband multiple-input multiple-output mobile-to-mobile channels is reviewed. To allow comparison between the proposed model and measured data, a new maximum likelihood based stochastic estimator is derived. The proposed estimator extracts the relevant model parameters from the measured data. The performance of the new estimator is evaluated by deriving the Cramer-Rao lower bound (CRLB) and by comparing the mean square error of the parameter estimates to the CRLB. Simulation results show that the proposed estimator has an asymptotically optimal performance, since it reaches the CRLB for a small number of samples.

A three-dimensional (3-D) analytical model for mobile-to-mobile communications is presented. From the analytical model, the envelope level crossing rate and average fade duration are derived for a 3-D non-isotropic scattering environment. The obtained analytical results are compared with measured data. The close agreement between the analytical and empirical curves confirms the utility of the proposed model.

A three-dimensional reference model for wideband multiple-input multiple-output (MIMO) mobile-to-mobile (M-to-M) channels is reviewed. To validate the reference model, an experimental MIMO M-to-M channel-sounding campaign was conducted for M-to-M vehicular communication with vehicles travelling along expressways in a metropolitan area. The measured data is processed and the channel statistics obtained from the reference model and from the empirical measurements are compared. The close agreement between the analytically and empirically obtained channel statistics confirms the utility of the proposed reference model.

Diversity can play an important role in the performance improvement of a communication system in fading channels. The achievable performance with signal space diversity (SSD) is analyzed and a closed form expression for the upper bound of average probability of bit error (Pb) for M-ary phase shift keying (MPSK) in Rayleigh fading channel is presented. The problem of calculating Pbof coherent MPSK over a Rayleigh fading channel has been studied previously in the literature. A solution based on the nearest neighbors was given. In this paper we show that the results with the nearest neighbor approximation represent an expurgated bound and are only valid for a small range of rotational angles. Exact pair-wise error probability (PEP) is derived for Rayleigh fading channels. It is shown that Gray signal constellation mapping is not necessarily the best option for a system employing coordinate interleaving and constellation rotation. Rotation angles are optimized by finding the minimum of the upper bound of Pb. It is shown that the new derived bound is tight for the entire range of rotational angles at high signal-to-noise ratio. Furthermore, the performance of the system in case of phase estimation error is also investigated by simulations.

Joint iterative channel and covariance estimation with sufficient-statistics (SS)-based chip combining is studied for a multicarrier code division multiple access (MC-CDMA) system operating under partial-band noise jamming (PBNJ). The expectation maximization (EM) algorithm, which exploits the log- likelihood ratio (LLR) from the decoder, is employed to estimate the channel impulse response and interference-plus-noise covariance matrix. The proposed chip combiner guarantees no loss of information in the soft output generated by the demapper. In our approach, the channel estimator or the chip combiner needs only the AWGN-plus-PBNJ power of each subcarrier to suppress jamming. Therefore, significant complexity reduction is achieved because the receiver does not need to estimate the jammer state information (JSI) and individual variances of AWGN and PBNJ on each subcarrier for chip combining. Simulation results demonstrate that the sufficient-statistic chip combiner (SSCC) always provides a smaller bit error rate (BER) than the minimum mean square error (MMSE) chip combiner.

A three-dimensional (3-D) theoretical model for wideband multiple-input multiple-output (MIMO) mobile-to- mobile (M-to-M) channels is presented. Based on this model, the statistical properties of wideband MIMO M-to-M channels are derived. In particular, the space-time-frequency correlation function, the power space-delay spectral density, and the envelope level crossing rate are derived for a 3-D non-isotropic scattering environment. Finally, to validate the theoretical derivations, some simulation results are presented and compared with measured data.

With single-carrier frequency-domain equalization, the carrier-frequency and sampling-frequency offsets are embedded in the phases of complex frequency-domain signal components. This paper proposes a sub-block processing to extract the phases and applies the least-squares regression to jointly estimate the offsets. The effectiveness of the proposed SC-FDE receiver is demonstrated on multipath fading channels.

An iterative pilot-symbol aided modulation (PSAM) channel estimation approach is proposed for vertical Bell Laboratories layered space-time (V-BLAST) orthogonal frequency division multiplexing systems operating on frequency-selective fading channels. Since the signals at the receive antennas are the superposition of signals from multiple transmit antennas, accurate channel estimates are crucial for good error performance. Furthermore, the time selectivity of the fading channels leads to inter-carrier interference (ICI). While ICI can be ignored for slow fading channels, it should be mitigated for fast fading channels. This paper proposes an ICI mitigation scheme for time-varying channels. We also propose an iterative channel estimator with low-complexity. Simulation results demonstrate the usefulness of the proposed algorithm on frequency-selective fading channels.

A three-dimensional (3-D) geometrical propagation model for wideband multiple-input multiple-output (MIMO) mobile-to-mobile (M-to-M) communications is proposed. Based on the geometrical model, a 3-D parametric reference model for wideband MIMO M-to-M multipath fading channels is developed. From the reference model, the space-time-frequency correlation function and the space-Doppler power spectral density are derived for a 3-D non-isotropic scattering environment. Finally, some simulation results are presented and compared with measured data. The close agreement between the theoretical and empirical curves confirms the utility of the proposed wideband model.

With single-carrier frequency-domain equalization (SC-FDE), the carrier-frequency offset (CFO) and sampling-frequency offset (SFO) are embedded in the phase rotations of the complex frequency-domain signal components at the output of the fast Fourier transform (FFT). To extract the phase rotations and estimate the CFO and SFO, the frequency-domain signal components need to be known. However, they are, in general, not known to the receiver, since they are a mixture of the data and pilot symbols. To solve this difficulty sub-block processing is proposed, such that joint estimation of the CFO and SFO can be applied. For the joint estimation, both the linear least-squares (LLS) and simple weighted least-squares (SWLS) regressions are considered, where the latter is shown to be robust to the channel frequency-selectivity. Finally, the SC-FDE receiver with proposed closed-loop tracking algorithm is tested on both quasi-static and time-varying multipath fading channels and its effectiveness is demonstrated.

Using a linear decomposition of continuous phase modulated (CPM) signals with tilted-phase, sufficient conditions are derived under whichM-ary partial-response CPM space-time codes will attain both full spatial diversity and optimal coding gain. A rank criterion forM-ary partial-response CPM that specifies the set of allowable modulation indices is identified. Furthermore, optimization of the coding gain for CPM space-time codes is shown to depend on the CPM frequency/phase shaping pulse, modulation index, and codewords. The modulation indices and phase shaping functions that optimize the coding gain are specified. Finally, optimization of CPM space-time codewords is discussed.

A three-dimensional (3-D) theoretical model for MIMO mobile-to-mobile (M-to-M) multipath fading channels is proposed and its spatial correlation function is derived. This correlation function is used to evaluate the effect of spatial correlation on the capacity of uniform linear antenna arrays. The effects of antenna spacing and antenna orientations on capacity are studied.

A three-dimensional (3-D) geometrical propagation model for multi-input-multi-output (MIMO) mobile-to-mobile (M-to-M) communications is proposed. Based on the geometrical model, a 3-D reference model for MIMO M-to-M multipath fading channels is proposed. From the reference model, a closed-form joint space-time correlation function is derived for a 3-D non-isotropic scattering environment and it is show that many existing correlation functions are special cases of the derived space-time correlation function.

A low-complexity iterative maximum a posteriori (MAP) channel estimator is proposed whose complexity increases linearly with the symbol alphabet size 'M. Prediction-based MAP channel estimation is not appropriate with a high-order prediction filter or a large modulation alphabet size, since the computational complexity increases with ML, where L is the predictor order. In contrast, the proposed channel estimator has a constant number of trellis states regardless of the prediction filter order, and is shown to provide comparable error performance to the prediction-based MAP estimator

In this paper, we investigate the effects of the spatial fading correlation on the performance of a multiple-input multiple-output (MIMO) adaptive antenna system with optimum combining (OC) in the presence of multiple cochannel interferers over a correlated Rayleigh fading channel. Based on the Khatri's distribution functions of quadratic forms in complex Gaussian random matrices, we develop a unified determinant representation of those joint eigenvalue distributions. Taking into account the spatial correlation among the antenna elements at the transmitter or receiver, we derive the closed-form formulas for the probability density function and outage probability of the maximum output signal-to-interference ratio (SIR) in an interference-limited MIMO-OC system. Furthermore, the average output SIR and error probability are also investigated. From numerical examples, we show that a new theoretical approach gives a simple and accurate way to assess the performance of the MIMO-OC system over arbitrarily correlated fading channels

Cooperation diversity schemes have been proposed for cellular networks that permit a base station (or a mobile station) to relay signals to a destination receiver, thereby increasing the network coverage and reliability. The mobile relays either decode and forward (DF) or amplify and forward (AF) the received signal. Most existing analyses of cooperation diversity assumes perfect channel information at the receiver. A realistic assessment should consider the effects of practical channel estimation schemes. This paper considers pilot symbol aided channel estimation for cooperation diversity systems. Since the overall channel in AF systems is different from conventional cellular channels, the channel estimation problem is interesting and challenging and therefore our focus is on AF systems. The paper addresses issues such as the estimator design, pilot symbol spacing based upon realistic channel models, and an approximate bit error rate (BER) analysis that accounts for imperfect channel estimation.

Conditions are derived under which M-ary full-response CPM space-time codes will attain full spatial diversity and optimal coding gain. General code construction rules are desirable due to the nonlinearity and inherent memory of CPM signals which make manual design or computer search difficult. Optimization of the coding gain for CPM space-time codes is shown to depend on the CPM frequency/phase shaping pulse, modulation index, and codewords. The modulation indices and phase shaping functions that optimize the coding gain are specified. Finally, optimization of ST-CPM codewords is discussed.

It is well-known that space-time block coded transmit diversity system suffers from a diversity penalty in the time-varying channel. Lately, based on the Alamouti two-input single-output (2ISO) antenna diversity system, Vielmon et al. investigated the impact of a time-varying channel on the bit-error-rate (BER) performance and also recommended three detectors to increase the system robustness for rapid channel variation. In this paper, we generalize these detectors and their BER expressions to the two-input multiple-output (2IMO) antenna configuration. Moreover, the bit-error-outages (BEOs) are also derived to provide a more objective judgment on the transmission quality within a fading environment. These generalized results can be easily extended to the orthogonal frequency-division multiplexing (OFDM) and code-division multiple-access (CDMA) systems with the 2IMO antenna configuration.

The performance of optimum combining is studied in a Rayleigh fading environment with arbitrary-power cochannel interferers and thermal noise. Based on the joint eigenvalue distributions of quadratic forms in complex Gaussian matrices, closed form expressions for exact moment generating function (MGF) of the output signal-to-interference-plus-noise ratio are derived. From the exact MGF, the moments of the output SINR and the symbol error rate of various M-ary moulation schemes are obtained. We verify the accuracy of our analytical results by numerical examples. The new analytical framework provides a simple and accurate way to assess the effects of equal and unequal-power cochannel interferers and thermal noise on the performance of optimum combining.

By approximating continuous phase modulated (CPM) signals with a small set of nonsymmetric nonorthogonal exponential functions, we have previously proposed a data-aided time and phase synchronizer that works well for all CPM schemes [1]. This paper extends this non-iterative data-aided synchronizer to its iterative decision-directed counterpart, for serially concatenated CPM systems. To prevent false locks in synchronization process, a preamble and pilot symbols are used in combination with the decision-directed technique. Simulation results show that the proposed turbo synchronizer is robust in acquiring and tracking both time-invariant and time-variant timing and phase errors at low signal-to-noise-ratios.

A theoretical model is proposed for multi-input-multi-output (MIMO) mobile-to-mobile (M-to-M) Rayleigh fading channels, such that the complex faded envelope does not depend on the distance between scatterers and antenna elements. From this model, a closed-form joint space-time correlation function is derived for 2-D non-isotropic scattering environment. Also, a space-frequency power density spectrum of the complex faded envelope is derived, assuming 2-D isotropic scattering environment. Finally, a statistical simulation model for MIMO M-to-M Rayleigh fading channels is proposed. The space-time correlation function of the simulation model is derived and verified by simulation, and an adaptive method for choosing the number of scatterers in simulations is proposed. The results show that the statistical simulation model is a good approximation of the theoretical model

A new statistical sum-of-sinusoids simulation model is proposed for mobile-to-mobile Rayleigh fading channels and compared with existing simulation models. The new proposed model has a lower variance of the auto-correlation functions, i.e., it converges faster and has a lower correlation between the in-phase and quadrature components of the complex faded envelope than existing simulation models. This model yields adequate statistics with only 30 simulation runs

A novel joint timing and phase-recovery technique is proposed for continuous phase modulation (CPM) systems based on Kalman filtering and an approximate representation of CPM signals with nonorthogonal exponential expansions (nOEE). Compared with existing techniques, the proposed synchronizer requires a less complex front-end processor, and can achieve reliable acquisition performance with a shorter preamble. The asymptotic stability and convergence of the proposed synchronizer is analyzed, including the effect of statistical channel-modeling errors on the convergence characteristics. The selection of suboptimal nOEEs and the design of triple-initialized Kalman filters are also discussed. Both theoretical and simulation results show that the proposed synchronizer is robust in acquiring and tracking both the time shift and the phase offset on either time-invariant or time-variant channels.

A performance analysis is presented for macrodiversity integrated voice/data CDMA systems. Macrodiversity with maximal ratio combining (MMRC) is ideal for such voice/data systems since it allows robust resource sharing between the two users while removing uncertainties in estimating the system capacity. Our analytical model allows the systems to dynamically allocate additional channels to data users to increase throughput when the necessary resource is available. The data users are characterized by arrival rates and average data size, and the resulting data user quality of service (QoS) performances are evaluated by using a simple birth-and-death Markov process. Our analytical results are fully verified by computer simulation. We show how various system QoS measures such as blocking and outage probabilities can be obtained and used in call admission control (CAC) decisions.

New sum-of-sinusoids simulation models are proposed for Rayleigh fading channels and compared with existing simulation models. First, an ergodic statistical ("deterministic") model is proposed that, compared to existing models, yields a significantly lower cross-correlation between different complex envelopes and between the quadrature components of each complex envelope. However, the auto-correlation functions of the quadrature components still do not match the theoretical functions. To overcome this disadvantage, we also propose a new statistical simulator that converges faster than existing statistical models, and has lower cross-correlations between different complex envelopes and between the quadrature components of each complex envelope. This new statistical model yields adequate statistics with only 30 simulation runs

A novel adaptive soft-input soft-output (A-SISO) module is developed for maximum a posteriori (MAP) symbol detection with parameter uncertainty. In contrast to the existing A-SISO algorithms that use linear prediction, the parameter estimation in the proposed structure is operated in a more general least-squares sense. Based on this scheme, a family of fixed-interval A-SISO (FI-A-SISO) algorithms is utilized to implement blind iterative phase synchronization for serially concatenated continuous phase modulation (SCCPM). For SCCPM systems, the forward-only FI-A-SISO algorithms are shown to be much more robust than the forward-backward FI-A-SISO algorithms in acquiring and tracking a time-varying carrier phase. The reason has to do with rotational invariance of CPM signals. This result can be extended to any rotationally invariant convolutional coded system with an unknown carrier phase.

A robust iterative pilot symbol aided modulation (PSAM) channel estimation (CE) approach is proposed for vertical Bell Laboratories layered space-time (V-BLAST) multiple-input multiple-output orthogonal frequency division multiplexing systems operating on time-varying wireless channels. Since the signals at receive antennas are the superposition of the transmitted signals from multiple transmit antennas in V-BLAST systems, accurate CE is crucial for good error rate performance. Furthermore, since the channel estimator is independently implemented for a MIMO system, the proposed iterative algorithm has an inherent iterative interference cancellation characteristic. Simulation results demonstrate excellent performance of the proposed algorithm on frequency selective fading channels

A novel joint timing and phase recovery technique is proposed for CPM systems based on Kalman filtering and an approximate representation of CPM signals with nonorthogonal exponential expansions (nOEE). In contrast to existing maximum likelihood methods that cannot synchronize partial response M-ary CPM signals, simulation results show that the proposed synchronizer is robust in acquiring and tracking both time shift and phase offset on either time-invariant or time-variant channels. Moreover, the asymptotic stability and convergence of the synchronizer is analyzed, including the effect of statistical channel modeling errors on the convergence characteristics.

Serially concatenated systems with rotational invariance (RI-SCS) can tolerate certain phase ambiguities and, therefore, for these systems coherent detection is robust even when cycle slipping, false-lock and hangup exist during phase synchronization. However, the convergence behavior of iterative phase synchronization and detection is still not well-understood. In this paper, we present a simplified phase model to analyze the convergence of iterative receivers with/without occurrence of phase rotations. Particularly, an oscillatory convergence behavior due to cycle slipping is explained by means of density evolution. Moreover, based on per-survivor processing (PSP) and single-estimator processing (SEP) techniques, a family of adaptive soft-input soft-output algorithms are employed to implement joint phase tracking and demodulation in the context of maximum a posteriori symbol detection. Both analytical and simulation results show that for RI-SCS the convergence performance of the SEP method is more robust than that of the PSP method when carrier phase has high and random dynamics.

Several new "sum-of-sinusoids" models have recently been introduced for the simulation of Rayleigh fading channels. These models are statistical in nature implying that their simulation parameters such as the Doppler frequencies are random. They have been shown to accurately reproduce some of the desired statistical properties of the faded envelope such as the time autocorrelation and the level crossing rate. However, a comparative analysis of these models, hitherto scattered throughout the literature, is not available. This paper compares these models in terms of their complexity and performance. The performance assessment is based upon the variance of the time average statistical properties from their ideal ensemble averages.

Mobile-to-mobile channels find increasing applications in futuristic intelligent transport systems, ad hoc mobile wireless networks, and relay-based cellular networks. Their statistical properties are quite different from typical cellular radio channels, thereby requiring new methods for their simulation. This paper proposes a "double-ring" model to simulate the mobile-to-mobile local scattering environment, and develops sum-of-sinusoids (SoS)-based models for simulating such channels. The proposed models produce waveforms having desired statistical properties with good accuracy, and also remove some drawbacks of an existing model derived by using the discrete line spectrum simulation method.

Iterative decoding and demodulation of bit-interleaved coded modulation (BICM) is investigated. The union bound on the error probability of BICM with maximum-likelihood (ML) decoding is derived with the assumption of a uniform interleaver. Based on the union bound, it is shown that an interleaving gain is achievable for BICM at high signal-to-noise ratio (SNR). The design rules on the symbol mapper for optimal asymptotic performance at high SNR are derived and a new symbol mapper, called the maximum squared Euclidean weight (MSEW) symbol mapper, is proposed with examples given for 8-PSK and 16-QAM. The MSEW mapper is shown by means of an extrinsic information transfer (EXIT) chart to provide the best error-floor performance for BICM at high SNR. At low SNR, a mapper doping technique is proposed that combines the MSEW mapper with Gray mapper to provide a good match to a given outer code. Simulation results are also presented to confirm our analysis.

A special complex sequence called a complex quadratic sequence is proposed as the frequency-spreading sequence for the multicarrier spread-spectrum (MC-SS) modulation scheme. The resulting MC-SS signal has constant envelope in both time and frequency domains. This feature provides flexibility for the MC-SS system to mitigate the effects of both partial-band and pulse jamming. For partial-band jamming, the MC-SS system with frequency domain detection and combining can outperform direct sequence spread spectrum. For pulse jamming, the MC-SS system with time-domain detection and combining can outperform other MC-SS systems. The proposed MC-SS signal has a constant envelope, thus, reducing linearity requirements on the power amplifier. A simple jammer state estimation scheme for both partial-band and pulse-jamming channels is also proposed. Furthermore, multiaccess with the MC-SS system is possible by assigning users different cyclic-shifts of the complex quadratic sequence.

Frequency-domain equalization for continuous phase modulation (CPM) is investigated. A discrete representation of the CPM signal is obtained by using the Gram-Schmidt orthonormalization procedure. The CPM discrete signal representation admits frequency-domain equalization for the purpose of mitigating intersymbol interference. General full- and partial-response CPM waveforms, and specific examples of MSK and GMSK with BT=0.3 are considered. Frequency-domain equalization is shown to be effective for CPM on severe frequency-selective fading channels.

The use of multiple input and multiple output (MIMO) antennas is a promising technique for increasing the capacity of wireless communication systems. Huge capacities are guaranteed only when channels between different transmitting and receiving antenna pairs are statistically independent. In this paper, we investigate the capacities of MIMO systems in a mobile-to-mobile environment by employing a "two ring" model which is simple extension of previous "one ring" model. With this model, we investigate the spatial correlation and information theoretic channel capacity of MIMO systems that use omni-directional antennas as well as MIMO systems with directional antennas. We show that MIMO systems with directional antennas yield good spatial decorrelation between antenna pairs even in a scarce scattering environment, while MIMO systems with omni-directional antennas suffer capacity degradation either when antennas are located closely each other, or when there is not enough multipath richness. Directional antennas guarantee the independence between different antenna pairs by not sharing scatterers, and the capacity is maximized by exploiting the independence between antenna pairs.

The BER degradation caused by imperfect channel estimation as well as the adverse effect of jamming on pilot symbols, which are used for the channel estimation (CE), is often neglected while analyzing OFDM und MC-CDMA systems leading to over-optimistic results. Therefore, to provide a more realistic analysis, we analyze the vulnerability of pilot symbol aided CE schemes for OFDM/MC-CDMA systems to narrowband and partial band jamming. We derive closed form BER expressions for studying the effect of imperfect CE for OFDMA/MC-CDMA in the absence of jamming in a frequency selective Rayleigh fading environment. We extend these results via simulations and theory (wherever permitted by mathematical tractability) to account for jamming. Some possible solutions such as the use of boosted pilots and the use of jamming side information, whenever available, to excise the jammed pilots or provide MMSE equalization are proposed to reduce the impact of jamming on the CE.

Orthogonal frequency division multiplexing (OFDM) is a popular method for high data rate wireless transmission. OFDM may be combined with antenna arrays at the transmitter and receiver to increase the diversity gain and/or to enhance the system capacity on time-varying and frequency-selective channels, resulting in a multiple-input multiple-output (MIMO) configuration. The paper explores various physical layer research challenges in MIMO-OFDM system design, including physical channel measurements and modeling, analog beam forming techniques using adaptive antenna arrays, space-time techniques for MIMO-OFDM, error control coding techniques, OFDM preamble and packet design, and signal processing algorithms used to perform time and frequency synchronization, channel estimation, and channel tracking in MIMO-OFDM systems. Finally, the paper considers a software radio implementation of MIMO-OFDM.

A new blind channel estimation scheme for orthogonal frequency division multiplexing systems is proposed based on the maximum likelihood principle. By avoiding the use of second- and higher-order statistics, a very fast convergence rate is achieved. A novel approach is also proposed for resolving the phase ambiguity of the blind channel estimate without the need for any reference symbols. The approach combines different modulation schemes on adjacent subcarriers, such as 3-phase shift keying (PSK) and quarternary PSK (QPSK), to resolve phase ambiguity. Simulations were performed for mobile radio environments with high Doppler frequencies and short-to-medium delay spreads. The achieved performance is comparable to that of pilot-based channel estimation for the case of QPSK-modulation.

Multicarrier delay diversity modulation (MDDM) is a scheme that uses orthogonal frequency division multiplexing (OFDM) on a "multipath" channel that is generated by using delay diversity. The full diversity criterion for MDDM is proven and illustrative examples of full-diversity codes are obtained based on the established criterion. Coding gains and interleaver designs are also considered and analyzed. Simulation results for MDDM on quasi-static flat and frequency-selective fading channels are discussed. MDDM is established as a strong competitive technique to existing space-time block codes and space-time tellis codes techniques for multiple input multiple output systems.

Multicarrier delay diversity modulation (MDDM) is a scheme that uses orthogonal frequency division multiplexing (OFDM) on a "multipath" channel that is generated by using delay diversity. The full diversity criterion for MDDM is proven and illustrative examples of full-diversity codes are obtained based on the established criterion. Coding gains and interleaver designs are also considered and analyzed. Simulation results for MDDM on quasistatic flat and frequency-selective fading channels are discussed. MDDM is established as a strong competitive technique to existing STBC and STTC techniques for MIMO systems.

A special complex sequence, called a complex quadratic sequence, is proposed as the frequency-spreading sequence for multicarrier spread spectrum (MC-SS) modulation scheme. The resulting MC-SS signal has constant envelope in both time and frequency domains. This feature provides flexibility for the MC-SS system to mitigate the effects of both partial-bond jamming and pulse jamming. For partial-band jamming, the MC-SS system with frequency domain detection and combining can outperform DS/SS. for pulse jamming, the MC-SS system with time-domain detection and combining can outperform MC-SS systems. The proposed MC-SS signal has a constant envelope thus reducing linearity requirements on the power amplifier. A simple jammer state estimation scheme for both partial-band and pulse jamming channel is also proposed and analyzed. Furthermore multi-access with the MC-SS system is possible by assigning users with different cyclic-shifts of the complex quadratic sequence. Simulation results are provided to verify our analysis.

This paper presents a maximum a posteriori (MAP) joint channel estimator and detector for convolutionally coded OFDM systems over mobile radio communication channels, which is suitable for turbo principles. To the purpose of the synchronization, the several papers where a known pilot-tone symbol [T.P. Holden and K. Feher, 1990], [P. Hoeher and F. Tufvesson, 1999] is transmitted simultaneously, were proposed. This pilot-tone symbol technique is applied to the channel estimation for OFDM systems, so that it gives the use of decision-directed algorithm based on the symbol-by-symbol MAP algorithm, which is optimal detection algorithm [L.R. Bahl et al., 1974] in terms of bit error rate (BER). However, in the presence of unknown quantities, since the symbol MAP algorithm is not optimal, the MAP algorithm, which is jointly linked with per-survivor processing (PSP) algorithm [R. Raheli, et al., 1995], is required. Instead of one 2-dimensional channel estimation scheme [P. Hoeher et al., 1997], two 1-dimensional channel estimation techniques with convolutional codes are presented in an iterative receiver structure. Hence, the proposed iterative joint estimation and detection algorithm gives the reliability values to the component decoder for convolutional codes, which is combined with pilot-tone technique, to obtain the better performance in the iterative way. Simulations demonstrate the performance of the proposed iterative joint channel estimator and detector.

Cascaded-integrator-comb (CIC) filters perform sample rate conversion (SRC) efficiently using only additions/subtractions. However, the limited number of tuning parameters may make conventional CIC filters unsuitable for SRC in software radio (SWR) systems. A simple modification to the CIC filter that enhances its SRC performance at the expense of requiring a few extra computations per output sample is proposed. Simulation results show that the modified CIC filter outperforms the conventional CIC filter for the purpose of SRC in SWR systems.

A new maximum a posteriori (MAP)-equivalent soft-input soft-output (SISO) algorithm is derived together with its simplified versions. The proposed SISO algorithms provide a good compromise between complexity and performance. Our simplest SISO algorithm has lower complexity than the log-MAP, the max-log-MAP, and the soft-output Viterbi (1998) algorithm SISO algorithms, and it is an equivalent max-log-MAP algorithm. When this algorithm is used, turbo codes with block length as short as 150 bits will outperform convolutional codes when compared on the basis of equal decoder complexity.

The reverse link performance of hierarchical wideband multicarrier code-division multiple-access (MC-CDMA) systems is studied. An MC-CDMA system divides the system bandwidth into several equal narrow subbands that are used to transmit multiple signal waveforms in parallel. MC-CDMA systems are known to be robust to multipath fading and narrowband interference. We propose a hierarchical MC-CDMA system where the microcell(s) occupies a fraction of the available subbands. It is shown that such an architecture is a viable way of supporting microcell traffic while protecting the existing macrocell traffic. The effects of microcell Nakagami fading and power control error are also studied.

A new sample rate conversion (SRC) method for software radio (SWR) systems is proposed. The method, which uses the window filter design and Lagrange functions, requires fewer computations than other SRC methods over a range of SRC factors for the wideband and high dynamic range signals that are typical of SWR systems. The computational requirements of the proposed SRC method and other SRC methods are compared and simulation results of the proposed method are discussed.

We present preamble and receiver design for a Q transmit L receive multi-input multi-output OFDM system. Tasks performed by the receiver are synchronization in time and frequency domains, followed by channel estimation and noise variance estimation. An algorithm is developed such that only Q OFDM symbols of a generalized length are required to perform functions of the preamble. Coarse time synchronization is performed using inherent periodicity in the preamble. Frequency offset estimation is then performed in the time domain, followed by residual frequency offset estimation in the frequency domain followed by fine time synchronization. The channel estimation algorithm is developed using least squares principle. Simulations are carried out for a broadband fixed wireless access scenario using a preamble with and without zero-padding of tones in the frequency domain.

A blind channel estimation scheme for OFDM is proposed. The algorithm is based on the ML-principle and features a very fast convergence rate. No reference symbols are needed to resolve the phase ambiguity. Simulations show the performance in mobile environments at high Doppler frequencies and short to medium delay spreads. The proposed approach maximizes the spectral efficiency by avoiding any reference symbols or pilots, and it minimizes the BER by using a non-differential modulation scheme.

Iterative decoding of bit-interleaved coded modulation (BICM) is analyzed. The interleaver of a BICM system is shown to provide not only time diversity gain as a channel interleaver, but also interleaving gain as a code interleaver. Our performance analysis of BICM assumes a uniform interleaver, and it is shown that the interleaving gain can be achieved at high SNR. The design rules on the symbol mapper are derived and a new symbol mapper design, called the maximum squared Euclidean weight (MSEW) symbol mapper, is presented for both 8-PSK and 16-QAM. Extensions to other signal constellations is straight forward. Simulation results confirm our analysis and show that BICM with MSEW symbol mapping achieves near Shannon limit performance.

Multiclass CDMA systems, which support multiple services with various quality of service (QoS) requirements, are studied. The focus is on the reverse link capacity and application of macrodiversity with maximal ratio combining (MMRC), where the signals from each mobile station (MS) are received by multiple base stations (BSs) and coherently combined. A simple analytical solution is first derived for the multiclass reverse link carrier-to-interference ratio (CIR). Using this CIR solution, a simple capacity analysis is developed in terms of the QoS requirements. Finally, the analysis is fully supported by simulation results.

Soft handoff has a special importance to power controlled code division multiple access (CDMA) systems. We introduce a new analytical model for CDMA soft handoff with emphasis on interference statistics at a system level. The relationship between soft handoff and power control is further explored by integrating power control error and shadowing correlation into the model. A new forward link model is also devised to study the effects of soft handoff on forward link performance. It is observed that the performance degradation due to power control error increases with increase in soft handoff region and higher shadowing correlation lowers the interference contribution from nonhandoff mobile stations (MS). It is also found that, unlike the reverse link, the forward performance depends on both given soft handoff setting and system load.

This paper proposes a time and frequency synchronization technique for a Q transmit and L receive (Q/spl times/L), MIMO OFDM system. The synchronization is achieved using training symbols which are simultaneously transmitted from Q transmit antennas. The training symbols are directly modulatable orthogonal polyphase sequences. The synchronization algorithm shows satisfactory performance even at a low SNR and in a frequency selective channel. The training sequence structure is specialized such that channel parameters in terms of channel coefficients and noise variance can be estimated once synchronization is achieved.

An analytical model for the extrinsic information of iterative max-log-MAP decoding of turbo codes is established based on a maximum probability approximation. The extrinsic information can be expressed as a Gaussian random variable with a mean and variance that are linear combinations of the received symbols. An important measure, called the effective weight, which is related to the pairwise error probability, is defined to explain the iterative decoding effect on a given code sequence. The evaluation of the pairwise error probability performance through decoder iterations can be calculated based on this model. The proposed approach can serve as a tool for the analysis of iterative max-log-MAP decoding.

Hierarchical wideband multicarrier CDMA (MC-CDMA) systems are studied. A MC-CDMA system divides the system bandwidth into several equal narrow subbands that are used to transmit multiple signal waveforms in parallel. MC-CDMA systems are known to be robust to multipath fading and narrowband interference. We propose a hierarchical MC-CDMA system where the microcell(s) occupies a fraction of the available subbands. It is shown that such an architecture is a viable way of supporting microcell traffic while protecting the existing macrocell traffic.

Wireless packet transmission requires an adaptive error control coding scheme that can accommodate varying code rate and very low FER requirements for high data rate transmission. Serial concatenated convolutional codes (SCCC) can provide lower FER performance than parallel concatenated convolutional codes (PCCC) in the region of moderate-to-high SNR because SCCC shows little error-flooring problem. This paper proposes a rate compatible punctured SCCC (RCPS) and RCPS-HARQ system to achieve adaptive and high reliable error control coding, and presents their performance on AWGN and multipath Rayleigh fading channels. Comparative results with rate compatible punctured PCCC (RCPP) and an example of a W-CDMA system are also given.

Hierarchical code division multiple access (CDMA) cellular systems, consisting of macrocells with underlying microcells, are studied. We seek power control schemes which will allow both hierarchical layers to share the same spectrum. For the reverse link, hierarchical maximal ratio combining (HMRC) is applied where each mobile station (MSs) is received and coherently combined by base stations (BSs) in both layers. For the forward link, selective transmit diversity (STD) is applied where each BS provides multiple transmit paths for MSs to choose. We show that both HMRC and STD are effective in hierarchical CDMA architectures. We conclude that hierarchical architectures are a viable solution for improving CDMA cellular system capacity, and a significant performance gain can be achieved without assigning disjoint spectrum between the layers, by utilizing macrodiversity schemes such as HMRC and STD.

Interleaved trellis-coded systems with full response continuous-phase modulation (CPM) are considered. Upper bounds on the bit-error rate performance are derived for coherent detection on the additive white Gaussian noise and flat Rayleigh fading channels by considering the trellis code, interleaver, and CPM modulator as a serially concatenated convolutional code. A coherent receiver that performs iterative demodulation and decoding is shown to provide good bit error performance. Finally, a noncoherent iterative receiver is proposed and is shown to perform close to the coherent iterative receiver.

A novel paging scheme under delay bounds is proposed for personal communication systems. This paging scheme is independent of the location probability distributions of the mobile users and satisfies the delay bounds, while minimizing the amount of bandwidth used for locating a mobile user. The proposed paging scheme includes the optimal partition algorithm and paging procedure with respect to paging costs and average delays. The numerical results demonstrate that the proposed scheme is very effective in the minimization of the paging costs for location probability conditions such as uniform and non-uniform distributions.

An optimal MAP equivalent SOVA decoding algorithm and its simplified suboptimal algorithm for non-binary codes are proposed. The implementation of its suboptimal algorithm is simpler, while its performance is very close to the optimal log-MAP algorithm. The proposed SOVA can be used as a decoder for turbo trellis coded modulation (TTCM). Simulation results for both the proposed SOVA and the log-MAP algorithms for TTCM and binary turbo codes are presented. It is concluded that the proposed SOVA performs very close to the log-MAP algorithm for both the TTCM and binary turbo codes, and its performance is better than the conventional SOVA.

A novel velocity estimation algorithm for cellular radio systems is presented. The algorithm assumes that the received signal can be modeled as the sum of finite number of complex exponentials. First the singular value decomposition (SVD) method is applied to the data matrix and a new matrix is formed for the signal space corresponding to the N largest singular values. A matrix pencil is formed from the eigenvectors of this new matrix. The complex exponents of the in-coming waves are obtained from the generalized eigenvalues of this matrix pencil. The algorithm obtains the velocity information from the maximum of the absolute values of the complex exponents/frequencies.

New paging schemes are presented for locating mobile users in wireless networks. Paging costs and delay bounds are considered since the paging cost is associated with bandwidth utilization and delay bounds influence call setup time. In general, location tracking schemes require intensive computation to search for a mobile terminal in current PCS networks. To reduce the paging cost, three new paging schemes-reverse, semi-reverse and uniform-are introduced to provide a simple way of partitioning the service areas and accordingly minimizing the paging cost based on each mobile terminal's location probability distribution. Numerical results demonstrate that our approaches significantly reduce the paging cost for various location probability distributions such as uniform, truncated discrete Gaussian, and irregular distributions.

This paper presents a joint channel coefficient and time-delay tracking technique for code-division multiple-access (CDMA) systems. Due to the highly nonlinear nature of time delay estimation, an iterative nonlinear filtering algorithm, called the "unscented filter" (UF), is employed. The UF can provide a better alternative to nonlinear filtering than the conventional extended Kalman filter (EKF) since it avoids errors associated with linearization. The Cramer-Rao lower bound is derived for the estimator, and computer simulations show that it provides a more viable means for tracking time-varying amplitudes and delays in CDMA communication systems than estimators based on the EKF.

This paper presents a performance analysis of the noncoherent delay lock loop (NC-DLL) in the presence of multiple-access interference (MAI). A renewal theory approach is applied along with the more familiar linear theory. The effect of the MAI on performance is evaluated in terms of the mean-time-to-lose-lock and the root-mean-square (RMS) tracking error. The analysis is made tractable by approximating the aperiodic cross-correlation function between two pseudonoise (PN) code sequences. The results are compared with those which assume that the MAI can be approximated as Gaussian noise. As expected, the results indicate a drastic decrease in performance as the number of users in a system is increased. The effect of the near-far ratio, PN code sequence length, system load, and signal-to-noise ratio on the performance of the NC-DLL in MAI are also examined.

Iterative demodulation and decoding of convolutionally encoded data is treated as a special case of the previously proposed serial concatenation of interleaved codes. It is shown that by exploiting the recursive nature of the differential modulation schemes (for example, DBPSK, DQPSK, CPM, etc.), large interleaving gains can be achieved similar to serial concatenation schemes. We also show that when memoryless modulation is used, precoding can be used to create a rate-1 recursive inner code in order to obtain interleaving gains without adding redundancy from the inner code.

List decoding of turbo codes is analyzed under the assumption of a maximum-likelihood (ML) list decoder. It is shown that large asymptotic gains can be achieved on both the additive white Gaussian noise (AWGN) and fully-interleaved flat Rayleigh fading channels. It is also shown that the relative asymptotic gains for turbo codes are larger than those for convolutional codes. Finally, a practical list decoding algorithm based on the list output Viterbi algorithm (LOVA) is proposed as an approximation to the ML list decoder. Simulation results show that the proposed algorithm provides significant gains corroborating the analytical results. The asymptotic gain manifests itself as a reduction in the bit error rate (BER) and frame error rate (FER) floor of turbo codes.

An iterative technique is developed for orthogonal frequency division multiplexing (OFDM) systems to mitigate the residual intersymbol interference (ISI) that exceeds the length of the guard interval. The technique, called residual ISI cancellation (RISIC), uses a combination of tail cancellation and cyclic restoration and is shown to offer large performance improvements. The effects of imperfect channel estimation are also considered. The RISIC algorithm is applied to a typical terrestrial high-definition television (HDTV) broadcasting system that uses a concatenated coding scheme for error control. Results show that the RISIC algorithm can effectively mitigate residual ISI on static or slowly fading ISI channels.

List decoding of turbo codes is analyzed under the assumption of a maximum-likelihood (ML) list decoder. It is shown that large asymptotic gains can be achieved on both the additive white Gaussian noise (AWGN) and fully interleaved flat Rayleigh-fading channels. It is also shown that the relative asymptotic gains for turbo codes are larger than those for convolutional codes. Finally, a practical list decoding algorithm based on the list output Viterbi algorithm (LOVA) is proposed as an approximation to the ML list decoder. Simulation results show that the proposed algorithm provides significant gains corroborating the analytical results. The asymptotic gain manifests itself as a reduction in the bit-error rate (BER) and frame-error rate (FER) floor of turbo codes.

A new algorithm is proposed for estimating the signal-to-interference plus noise ratio S/(I+N) in time-division multiple-access (TDMA) cellular systems. The S/(I+N) estimator is evaluated for use in the IS-54/136 system and a GSM-like system, and compared with existing techniques. The algorithm has a mean square prediction error that is comparable to the best known S/(I+N) estimation schemes, but with a significantly reduced computational complexity.

This paper presents two equalizer structures for trellis-coded continuous phase modulation (TC-CPM) on multipath fading intersymbol interference (ISI) channels. An equivalent discrete-time (DT) model is developed by combining the tapped-delay-line (TDL) model of the frequency-selective channel and by oversampling at the receiver. The (noninterleaved) fractionally spaced maximum-likelihood sequence estimation (MLSE) equalizer performs continuous phase modulation (CPM) demodulation, trellis-coded modulation (TCM) decoding, and channel equalization by exploiting the finite state nature of the ISI-corrupted TC-CPM signal. Both simulation and analytical results show diversity-like improvement when performing joint MLSE decoding and equalization. For the interleaved soft-output equalizer, the soft symbol metric is delivered to the TCM decoder by using a forward and backward recursion algorithm. Three variants of the soft-output equalizer are examined. We conclude that the backward recursion is essential to partial response CPM schemes, and with moderate complexity, the soft-output equalizer can have a substantial advantage over a noninterleaved MLSE equalizer.

Switched beam smart antennas are shown to either increase the capacity or extend the radio coverage of cellular systems, by increasing the carrier-to-interference ratio. The trunking efficiency degradation caused by narrow beam sectoring can be recovered or even improved by using a variety of trunkpool techniques. One drawback of switched beam smart antennas is that uplink performance is not uniform over the entire cell area, and this presents a limiting factor on the achievable gains.

Two soft-limiter RAKE receivers are evaluated for coded direct-sequence/differential phase shift keying (DS/DPSK) signaling over a pulse jammed multipath-fading channel that use a combination of antenna and multipath diversity. One uses predetection selective (antenna) combining followed by postdetection equal gain (multipath) combining, and the other uses postdetection equal gain combining only. In either case, the postdetection diversity combiner output is soft-limited prior to decoding. It is shown that for increasing levels of diversity the soft-limiter becomes quite effective, resulting in a receiver performance that approaches a maximum likelihood (ML) soft decision receiver with perfect jammer state information.

A noncoherent receiver is proposed for partial response trellis-coded continuous phase modulation (TC-CPM) on interleaved flat Rician-fading channels. By using a multiple-symbol observation interval and a simple metric calculator, the power efficiency is improved over a receiver that uses a single-symbol observation interval. Performance bounds on the bit error probability are derived by defining a set of characteristic distances for CPM signals, and showing that TC-CPM is equivalent to a TCM scheme. Our results show that, with the same observation length, the proposed receiver is less than 0.5 dB inferior to a coherent receiver for which perfect channel information is needed. We also conclude that in terms of joint power-bandwidth complexity, 2RC is the best candidate for rate-1/2 TCM codes.

In-service interference plus noise power (I+N) and signal-to-interference plus noise power SI(I+N) estimation methods are examined for TDMA cellular systems. A simple (I+N) estimator is developed whose accuracy depends on the channel and symbol estimate error statistics. Improved (I+N) and S/(I+N) estimators are developed whose accuracy depends only on the symbol error statistics. The proposed estimators are evaluated through software simulation with an IS-54 frame structure. For high speed mobiles, it is demonstrated that S/(I+N) can be estimated to within 2 dB in less than a second.

A radio location method for code-division multiple-access (CDMA) microcellular networks is investigated. The method discussed focuses on the use of time difference of arrival (TDOA) estimates for deriving the position of a mobile unit in a CDMA system, where the transmitted signal is received by several base stations (BSs). The TDOA estimates are obtained by using a delay-lack loop. A similar method is used in the global position system (GPS), but its performance in an urban microcellular propagation environment has not been previously studied. Simulation results are given for different radio propagation environments.

A new receiver structure is proposed €or trellis- coded modulation on multipath fading intersymbol interference (ISI) channels that permits the use of large-state trellis codes. The receiver uses a sequential sequence estimator With the Fano algorithm, and a channel estimator consisting of a fast nom- cursive start-up algorithm for training and the LMS algorith for tracking. During the tracking mode, the channel estimates are updated dynamically by using recent tentative decisions produced by the sequential sequence estimator. This approach results in good tracking even on rapidly varying channels, and reduces the degradation in performance of the sequential sequence estimator due to channel estimation error. The effect of fading is mitigated using both implicit time diversity in the form of interleaved trellis-coded modulation and explicit antenna diversity.

A new tracking loop is proposed for direct-sequence spread-spectrum signaling on a frequency-selective fading channel. By exploiting the inherent multipath diversity of the channel, the new tracking loop overwhelmingly outperforms a traditional noncoherent delay-locked loop (DLL) for all cases under consideration. Linear and nonlinear (based on the renewal process approach) methods are employed to analyze the new tracking loop with perfect channel estimation. Although the analytical methods are developed under the guise of a slowly time-varying channel, the analytical and simulation results show close agreement for channels with a code Doppler shift /spl beta//sub D/ as large as 0.117598 (Doppler shift f/sub D/=83 Hz). Consequently, the analytical methods, especially those based on linear methods, can be easily employed to characterize the new tracking loop. The performance degradation caused by imperfect channel estimation is determined by computer simulations. Over a range of signal-to-noise-ratios (SNRs) of practical interest, the simulation results show a degradation of about 2 dB and 1 dB for /spl beta//sub D/=0.0117598 (f/sub D/=8.3 Hz) and /spl beta//sub D/=0.117598 (f/sub D/=83 Hz), respectively.

This paper discusses the use of mobile cellular radio networks for providing vehicle location information to intelligent vehicle/highway system (IVHS) services. We review various automatic vehicle location (AVL) techniques in context to their application in a direct-sequence code-division multiple-access (DS/CDMA) system, in particular, the EIA/TIA/IS-95 standard proposed by Qualcomm Inc. A new matched filter location technique which is suited to the CDMA environment is discussed along with simulated error statistics and recommendations for improvement. We also consider network loading effects in terms of Signaling System 7 (SS7).

The paper describes a new Japan digital cellular receiver that uses an adaptive truncated maximum-likelihood sequence estimation (MLSE) equalizer. The receiver employs a channel estimation and symbol synchronization procedure that uses the known phase shifts between successive symbols in the synchronization word. Per-survivor processing is used to track the channel variations and carrier frequency offset. Simulation results are presented for multipath Rayleigh fading channels having various delay profiles. Comparisons between a regular symbol-spaced truncated MLSE receiver and a fractionally-spaced truncated MLSE receiver are also furnished.

Channel assignment schemes are evaluated that are suitable for the large scale uncoordinated deployment of in-building PCS microsystems in a dense urban area. Three fully distributed dynamic channel assignment strategies are evaluated by computer simulation in terms of their call blocking probabilities. Baseline comparisons are made to a fixed channel assignment scheme that assigns channels with complete knowledge of the interference neighbourhoods and traffic loading of the microcells. The best identified DCA scheme uses a weighted channel ordering with channel rearrangements. This is followed by a DCA scheme that use simple channel orderings with channel rearrangements and, finally, by a random DCA scheme.

A novel class of direction biased handoff algorithms are proposed for improving the handoff performance in urban microcells. Multi-cell urban microcell handoff properties are derived for a cell layout with base stations at every other intersection. The direction biased handoff algorithms are shown to improve cell membership properties and handoff performance by lowering the mean number of handoffs while simultaneously reducing the handoff delay. A direction estimation technique based on the signal strength history is shown to provide improved handoff performance, especially for line of sight handoffs.>

Systematic trellis-coded modulation (STCM) is a novel approach to coded modulation, which enables symbol-by-symbol detection of trellis-coded data. A set of design rules, which guarantees nonzero coding gain, and codes with asymptotic coding gains of 3.0-5.4 dB are presented. STCM is well suited for operation in a dual-mode receiver. During normal operation the receiver uses a sequence estimation algorithm such as MLSE or SSE. When the channel introduces severe distortion, as is the case during a deep fade, the decoder switches to a systematic decoding algorithm, which is simple to implement, and guarantees BER performance that is better than uncoded modulation. The authors demonstrate the performance of various STCM codes with a dual-mode receiver on multipath fading channels.>

A sequence acquisition scheme based on sequential estimation and soft-decision combining methods is proposed and analyzed for direct-sequence CDMA systems employing Kasami sequences. The proposed technique is effective for Kasami (1987) sequences having very long periods. The algebraic properties of Kasami sequences are exploited to provide a very reliable estimate of the correct phase of the local shift register before tracking is attempted. This estimate is obtained by generating and combining multiple statistics for each chip that comprises the initial phase estimate. Expressions are derived for the mean and variance of the acquisition time, and the probabilities of acquisition, false dismissal, and false alarm. The proposed scheme compares well with the performance of alternative parallel acquisition schemes.>

A method is presented for upper bounding the error probability of trellis-coded modulation on multipath-fading ISI channels that uses one-directional stack algorithm. The method provides a tighter upper bound than transfer function bounding techniques, and is useful for large-state systems, because the transfer function is not required. The stack algorithm exploits the symmetry properties of the trellis code to reduce computing time.>

A renewal process approach is used to analyze noncoherent delay-locked loops (DLLs) for spread spectrum systems operating over frequency selective and frequency nonselective slow fading channels. The effects of multipath fading are evaluated in terms of the mean-time-to-lose-lock (MTLL) and the root-mean-square (RMS) tracking error. For channels that have a specular component, the following results are observed: (i) the effect of multipath fading is more significant for tracking loops that have large loop signal-to-noise ratios (SNRs); (ii) a smaller early-late discriminator offset /spl Delta/, which is bounded by 0 0.5) may result in a higher MTLL, especially if there is a strong multipath effect. From (ii) and (iii), instead of using the popular choice of /spl Delta/=0.5, a larger /spl Delta/ may be chosen for a DLL that works at low SNRs and/or strong multipath fading environments, where MTLL is an important consideration. >

The uplink and downlink performance of a digital cellular radio system that uses direct sequence code division multiple access is evaluated. Approximate expressions are derived for the area averaged bit error probability while accounting for the effects of path loss, log-normal shadowing, multipath-fading, multiple-access interference, and background noise. Three differentially coherent receivers are considered: a multipath rejection receiver, a RAKE receiver with predetection selective diversity combining, and a RAKE receiver with postdetection equal gain combining. The RAKE receivers are shown to improve the performance significantly, except when the channel consists of a single faded path. Error correction coding is also shown to substantially improve the performance, except for slowly fading channels.>

The error probability of reduced-state sequence estimation (RSSE) for trellis-coded modulation (TCM) on intersymbol interference channels is evaluated. A method based on a stack algorithm is proposed to evaluate the union bound on the error probability for ideal RSSE, which is a good approximation to the error probability of real RSSE. The stack algorithm is employed because it provides a good tradeoff between computer memory and computing time.>

The performance of ideal reduced-state sequence estimation (RSSE) (without error propagation) is known as a good approximation to the performance of real RSSE. In the literature, the minimum distance of ideal RSSE has been employed for approximating the error probability of real RSSE. However, this approximation can be very poor, even though the system has a large signal-to-noise ratio. In this work, a union upper bound on the error probability for ideal RSSE is used to approximate the true error probability. This union bound provides a better approximation than the minimum distance. A new method based on a stack algorithm and a subset-error state diagram is proposed for calculating this union bound. The stack algorithm is employed because it provides a good tradeoff between computer memory and computing time.>

The performance of a multiple-cell direct-sequence code division multiple-access cellular radio system is evaluated. Approximate expressions are obtained for the area-averaged bit error probability and the area-averaged outage probability for both the uplink and downlink channels. The analysis accounts for the effects of path loss, multipath fading, multiple-access interference, and background noise. Two types of differentially coherent receivers are considered: a multipath rejection receiver and a RAKE receiver with predetection selective combining. Macroscopic base station diversity techniques and uplink and downlink power control are also topics of discussion.>

The performance of a receiver using a combined MLSE (maximum likelihood sequence estimation) equalizer/decoder and D-diversity reception is analyzed for multipath Rayleigh fading channels. An upper bound on the (decoded) bit error probability is derived. Comparisons to simulation results show that this upper bound is quite tight when the system has a high signal-to-noise ratio or when diversity reception is used. The upper bound involves an infinite series that must be truncated at a point where the remainder can be safely assumed to be small. An algorithm based on a one-directional stack algorithm is proposed for this calculation because it makes efficient use of computer memory.>

An examination is made of the performance of type-I hybrid ARQ (automatic repeat request) protocols in a slotted direct-sequence CDMA (code-division multiple access) network operating in a hostile jamming environment. The network consists of an arbitrary number of transceivers arranged in a paired-off topology. The traffic arrival process is derived by means of a Markov model. Throughput-delay expressions are derived in terms of the channel cutoff rate and capacity. The effects of jammer state information are discussed. Network design parameters are identified and their dependency on system parameters is examined in detail. It is shown that, for a given population size, traffic intensity, and bit energy/jammer noise ratio, there is an optimal probability of retransmission, code rate, and processing gain that maximizes network performance in the presence of worst-case pulse jamming.>

A link throughput analysis is presented for a slotted frequency-hop multiple-access (FHMA) packet radio network (PRN) operating in the presence of background noise, partial-band noise jamming, and partial-band tone jamming. The PRN consists of an arbitrary number of transceivers arranged in a paired-off topology. Forward error-correction coding is used for packet protection. M-ary FSK modulation is used with hard-decision decoding. Expressions are derived for the link throughput in terms of the channel cutoff rate and capacity. The dependency of the optimal processing gain, code rate, and jamming fraction on the population size, traffic intensity, bit energy to background noise ratio, and bit energy to jammer noise ratio is examined in detail. It is shown that a properly designed (optimized) PRN using random-access FHMA offers a significantly larger heavy-load throughput than a random-access frequency-division multiple-access PRN.>

The effectiveness of antenna and spread-spectrum diversity is evaluated for direct-sequence differential phase-shift-keyed signaling over a worst-case pulse-jammed multipath-fading channel. Two diversity combining techniques are proposed. One uses predetection selective combining followed by postdetection equal-gain combining, and the other uses only postdetection equal-gain combining. The use of coding with hard and soft decision decoding is also considered. It is shown that the proposed diversity techniques can provide a significant improvement in the performance of coded antijam systems operating over jammed multipath-fading channels.>

The performance of a soft-limiter metric and a quantized soft-limiter metric is evaluated for coded DS/DPSK (direct sequence/differential phase shift keying) in the presence of worst case pulse jamming and background noise. The metrics are easy to implement and do not require jammer state information. Instead they rely on the use of receiver thresholds, which must be adjusted according to the code rate and the received bit-energy-to-background-noise ratio. The performance of the metrics is evaluated by using the cutoff rate criterion and a number of specific convolutional and block codes. It is shown that the metrics can offer a significant soft-decision decoding gain and can perform to within 0.5-1.5 dB of the maximum-likelihood soft-decision metric with perfect jammer state information.>

The performance of hybrid automatic repeat-request (ARQ) protocols in slotted direct-sequence code-division multiple-access networks is analyzed. A Markov model is used to derive throughput-delay expressions in terms of the channel cutoff rate and capacity. Network design parameters are identified and their dependency on systems parameters is examined in detail. It is shown that, for a given population size, traffic intensity, and ratio of bit energy to background noise, there is an optimal probability of retransmission, code rate, and processing gain that maximizes performance. The stability of the network is also discussed.>

For pt.1 see ibid., vol.COM-35, p.1329-41 (1987). A performance evaluation is presented for selective diversity with feedback for frequency-hopping M-ary frequency-shift-keyed systems operating over Rayleigh faded channels in the presence of partial-band noise and partial-band tone jamming. The behavior of uncoded and coded systems is studied. For coded systems, the performance is evaluated for hard-decision receivers without channel state information and soft-decision receivers with perfect jammer state information. The results demonstrate that the performance of uncoded FH/MFSK with selective diversity is unacceptable. However, this diversity technique can offer definite improvements for coded FH/MFSK systems. Specifically, the effectiveness of selective diversity signaling depends on the provision of a feedback channel between the transmitter and receiver to provide the transmitter with the fading gains of the independently faded channels. To obtain an improvement from the selective diversity signaling scheme described here, there must be multiple independently faded channels between the transmitter and receiver. If not, the performance of the selective diversity signaling scheme will be identical to the performance of FH/MFSK without diversity.>

The authors present a feedback rate control technique for FH/BFSK (frequency-hop/binary phase-shift keying) signaling over a jammed flat-flat fading channel. An algorithm is developed for tracking the channel fade level, dynamically adjusting the transmitted data rate, and mitigating the effects of partial-band noise jamming. Simulation studies indicate that improvements of about 2 dB can be obtained in the coded performance with the proposed adaptive rate system, when compared to a nonadaptive system operating over the same communication medium with identical power and bandwidth resources.>

This paper gives an evaluation of the performance of adaptive signaling techniques for jammed fading channels. These techniques perform remarkably well for fading channels with AWGN. The performance of both uncoded and coded systems is examined in the presence of jamming. Adaptive signaling schemes are shown to offer little improvement for uncoded antijam systems. However, for coded antijam systems, they provide improvements in the performance and, in some cases, simplify the receiver implementation.

The performance of diversity and/or coding is evaluated for FH/MFSK signaling over Rayleigh fading channels in the presence of jamming. The effects of partial-band tone and partial-band noise jamming on uncoded and coded systems are considered. The results indicate that FH/MFSK signaling with diversity provides satisfactory performance for jammed fading channels. For coded FH/MFSK signaling over fading channels, noise jamming may be more effective than tone jamming. The amount of improvement resulting from the use of diversity in conjunction with coding depends upon many factors, including the nature of the channel, the degree of channel state information available at the decoder, the type of decoding, and the modulation alphabet size.