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Detection of the frequency-hopping (FH) signal is challenging when the hopping rate is unknown. Conventional spectrogram-based schemes can detect FH signals, but its performance is limited by the time-frequency resolution trade-off and spectral leakage. To alleviate this issue, we design convolutional neural network (CNN) and hybrid CNN/recurrent neural network (RNN)-based schemes. The CNN-based scheme alleviates spectral leakage by using feature maps. The hybrid CNN/RNN-based scheme mitigates the time-frequency resolution trade-off by using feature maps extracted from spectrograms of various window lengths. In simulations, the hybrid CNN/RNN-based scheme is shown to outperform the CNN-based and conventional detection schemes.

Small cell is one of the key technologies in modern wireless communications, extending cell coverage and providing capacity increment. However, challenges still exist in realizing and optimizing the small cell networks. In this letter, we propose a distributed iterative threshold control scheme with minimal increase in hardware complexity to improve the energy efficiency of sleep mode control by reducing the number of unbeneficial mode transitions. We also show that the proposed scheme provides improved system adaptability to network traffic time-variation compared with conventional sleep mode control schemes.

In practical wireless relay communication systems, nondestination nodes are assumed to be idle not receiving signals while the relay sends messages to a particular destination node, which results in reduced bandwidth efficiency. To improve the bandwidth efficiency, we relax the idle assumption of non-destination nodes and assume that non-destination nodes may receive signals from sources. We note that the message relayed to a particular node in such a system gives rise to interference to other nodes. To study such a more general relay system, we consider, in this paper, a relay system in which the relay first listens to the source, then routes the source message to the destination, and finally produces interference to the destination in sending messages for other systems. We obtain capacity upper and lower bounds and study the optimal method to deal with the interference as well as the optimal routing schemes. From analytic results obtained, we find the conditions on which the direct transmission provides higher transmission rate. Next, we find the conditions, by numerical evaluation of the theoretical results, on which it is better for the destination to cancel and decode the interference. Also we find the optimal source power allocation scheme that achieves the lower bound depending on various channel conditions. We believe that the results provided in this paper will provide useful insights to system designers in strategically choosing the optimal routing algorithms depending on the channel conditions.

Notable changes in the next-generation wireless communication system include the fact that the nominal height of base-station antennas becomes lower than the height of typical rooftops. In this scenario, reflection and scattering of waves become more dominant than diffraction in short-range propagation. We first analyze the reflection and scattering loss of propagation by using ray-tracing simulation, and on the basis of the analysis, we propose a propagation prediction model based on geometric optics in the urban street canyon scenario. The proposed model is defined by geometrical parameters such as the street width and the distance to a corner, such that the model can be applied to various environmental scenarios. It can also simultaneously predict propagation losses in many corners. The proposed model is justified with measurement data.

We address secure vehicle communication using secrecy capacity. In particular, we research the relationship between secrecy capacity and various types of parameters that determine secrecy capacity in the vehicular wireless network. For example, we examine the relationship between vehicle speed and secrecy capacity, the relationship between the response time and secrecy capacity of an autonomous vehicle, and the relationship between transmission power and secrecy capacity. In particular, the autonomous vehicle has set the system modeling on the assumption that the speed of the vehicle is related to the safety distance. We propose new vehicle communication to maintain a certain level of secrecy capacity according to various parameters. As a result, we can expect safer communication security of autonomous vehicles in 5G communications.

ITU-R has defined IMT-2020 as a new standard name for fifth generation mobile systems and has set the minimum performance requirements and evaluation methodologies of IMT-2020. IMT-2020 systems will be the mobile systems that include new radio interface which support the new capabilities of systems beyond IMT-Advanced. In particular, the data rate of IMT-2020 is expected to be 10 times to 20 times larger compared to IMT-Advanced for enhanced Mobile Broadband. In order to achieve the IMT-2020 data rate requirements, the use of mmWave band and micro-cell deployment is essential. In this paper, we evaluate the theoretically expected data rate of urban micro channel model by downlink 2×2 MIMO system level simulation. When the micro-cells are deployed over the macro-cells layout, the expected data rate is about 3.9Gbits/s, which is 5 times larger than only macro-cell scenario.

To evaluate 4G cellular systems, a system-level simulation (SLS) with the ITU-R channel model is often used. For the evaluation of the next generation communication systems, a SLS including a device-to-device (D2D) system is needed. However, as the number of multi-paths in a D2D link is squared compared to the link between a base station and a mobile station, the simulation run-time has to increase greatly. In this paper, we propose the ITU-R channel model extension to the D2D channel and the Doppler response-based fast fading channel generation as a realization method for the D2D channel. The proposed method can significantly reduce the simulation run-time.

In this paper, we analyze a 28 GHz suburban channel using a hybrid ray-tracing simulation. Hybrid ray-tracing technique is a combination of image method and shooting-and-bouncing rays (SBR) method. The SBR method finds a rough propagation path and the image method predicts the exact propagation path. The hybrid ray-tracing simulation is compared with a measurement campaign conducted in Wolpyeong-dong, Daejeon, Korea, and its performance is verified. The transmitter is placed on a 29m building; the heights of the other buildings are between 10m and 12m. Based on a reasonable agreement between the results of ray-tracing and the measurement results, five streets of Wolpyeong-dong were analyzed using ray-tracing simulation. The path loss, power delay profile, root mean square delay spread, angle of arrival and angular spread were obtained.

This paper proposes an admission control algorithm for cellular networks based on the direct and dynamic monitoring of quality of services (QoS) performance metrics--both system delay tail and residual throughput. The main purpose of directly monitoring these QoS performance metrics is to more precisely meet the QoS requirements. The delay tail is efficiently estimated by the proposed algorithm and the total residual throughput is determined based on the total achieved throughput and total required throughput. With the estimated delay tails and measured residual throughput, the admission or rejection of a new user is determined at each base station. By doing so, the admission control algorithm improves resource utilization by guaranteeing the QoS. Additionally, the cellular system becomes more robust against the time-varying fading channel environment. The simulation results of the long term evolution downlink system show that the proposed algorithm can achieve a significant improvement in results compared to those of reference schemes. A general Neyman---Pearson-like framework is also used in evaluating the various admission control mechanisms.

In order to reflect a realistic wireless channel as closely as possible, the channel model becomes very complicated and is thus prone to error when implemented as a channel simulator. However, there is no rigorous way of verifying the implementation of the channel simulator. We propose a novel verification methodology that aims at implementing a verified channel simulator for the IMT-Advanced channel model. We first derive a systematic description of the channel model, where a random waveform is generated through various deterministic functional blocks and independent random number generators. We then verify the deterministic functional blocks by adopting the vector-based software verification methodology.

We consider a queuing model with applications to electric vehicle (EV) charging systems in smart grids. We adopt a scheme where an Electric Service Company (ESCo) broadcasts a one bit signal to EVs, possibly indicating ‘on-peak’ periods during which electricity cost is high. EVs randomly suspend/resume charging based on the signal. To model the dynamics of EVs we propose an M/M/∞ queue with random interruptions, and analyze the dynamics using time-scale decomposition. There exists a trade-off: one may postpone charging activity to ‘off-peak’ periods during which electricity cost is cheaper, however this incurs extra delay in completion of charging. Using our model we characterize achievable trade-offs between the mean cost and delay perceived by users. Next we consider a scenario where EVs respond to the signal based on the individual loads. Simulation results show that peak electricity demand can be reduced if EVs carrying higher loads are less sensitive to the signal.

In this paper, we propose a scheme, called Video Packet Adaptation Layer (VPAL), for reliable video multicast over the IEEE 802.11n WLAN. VPAL is composed of (1) Raptor coding for reliable video transmission, (2) header compression and (3) packet aggregation, both for efficient video transmission. Most of the VPAL functionalities reside above the emerging IEEE 802.11n Medium Access Control (MAC) layer while the packet aggregation requires some changes in the MAC functionalities. The reliability of the video multicast under a strict delay requirement, is provided by achieving the target error probability of video packets, which is done by controlling both the Raptor code rate and the physical (PHY) layer transmission rate. This strategy can provide a satisfactory quality of multicast video service irrespective of the channel condition with a minimum bandwidth use. New features of the 802.11n MAC are utilized for the channel status feedback from the users. Redundant header fields in the video packets are compressed, and then these packets are aggregated to further reduce the protocol overheads. We also consider a reduced version of VPAL which does not require any change in the MAC functionalities and simply works with the IEEE 802.11n MAC. The performance of the proposed systems is comparatively evaluated in terms of the perceived video quality, i.e., peak signal-to-noise ratio (PSNR), as well as the amount of required resources via both numerical analysis and simulations.

We study the tradeoff between energy and bandwidth efficiency for short packet-transmission systems for wireless sensor networks. Using random coding bound (RCB) analysis, we show that 16-ary and 32-ary orthogonal modulation schemes provide reasonable balance between energy and bandwidth efficiency. In addition, we compare various channel-coding schemes and conclude that convolutional codes are well suited for wireless sensor network applications having excellent performance and reasonable robustness to imperfections, such as estimation errors.

Automatic Repeat reQuest (ARQ) is a very effective technique against transmission error at the medium access control (MAC) layer. An erroneous MAC protocol data unit can be typically retransmitted within a given limit. In order to improve the IP-level performance, which directly affects the user-perceived quality-of-service (QoS), we propose a new truncated ARQ strategy, called MAC service data unit-based ARQ (S-ARQ), where the finite number of opportunities for retransmissions are shared by multiple fragments out of an IP datagram. We describe how S-ARQ can be implemented in a practical system, and then propose another variant of S-ARQ employing a functionality called early detection of failure. Basically, we evaluate the performance of S-ARQ in two different manners. First, assuming i.i.d. error process, we analyze both the probability of the delivery failure and the average delay of IP datagram. Then, we assess the performance of S-ARQ via simulation over a 2-state Markov channel.

This letter deals with coding and multiplexing strategies for DL/UL MAP transmission in IEEE 802.16m. Separate coding gives a better choice against the joint coding due to the individual users' link adaptation gain. As a multiplexing option, frequency-domain multiplexing outperforms time-domain one in the system-level performance thanks to its flexible power sharing capability between overhead channels and user traffic channels. Overall system-wide performance results are presented with the system level simulation for the various options.

IEEE802.16m standard is based on the MIMO-OFDM technology to provide high speed packet data service both in downlink and uplink. For the downlink broadcasting of control information, in order to extend the coverage of a cell, the nominal operating point should be set for the user at the edge of a cell, and no feedback should be used. For broadcasting that information, the MIMO technology should take a transmit diversity form targeted for low SNR. Several transmit diversity schemes are presented and preferable modes of operations for the broadcasting channel are proposed with numerical analysis.

The information-theoretic sum capacity of reverse link CDMA systems is investigated in this paper. As the reverse link CDMA systems are interference-limited, for given channel and noise conditions, the information-theoretic system capacity can be achieved by optimally allocating the transmit powers of the mobile stations. The maximum capacity is often achieved by unfair resource allocation. To avoid such a case, QoS constraints are imposed to individual mobile stations. The exhaustive search of the optimal power allocation solution that maximizes the aggregate capacity, requires O(N/sup M/) computations, where M is the number of the mobile station in the system and N is the granularity of the transmit power of a mobile station. The paper shows that for a single cell, the optimal power allocation solution can be found by polynomial times of computations, without sacrificing the optimality. Numerical results are presented to show the multi-user diversity gain and the impact of QoS constraints.

This article describes enhancements to the physical layer design of single-carrier (1/spl times/) cdma2000/sup /spl reg// wireless networks introduced by Revision C of the IS-2000 standard (commonly referred to as 1/spl times/EV-DV). These improvements are mainly for the support of high-speed wireless packet data service on the forward (base station to mobile station) link. A new shared channel, the forward packet data channel, F-PDCH, is introduced to significantly increase spectral efficiency. This is accomplished through smart, channel-dependent scheduling of base station, BS, resources by taking advantage of the delay-tolerant nature of data traffic. This shared channel utilizes fast link adaptation through adaptive modulation and coding supported by the feedback of channel quality information. A form of hybrid ARQ type II technique commonly referred to as asynchronous adaptive incremental redundancy compensates for frame error events due to imperfect link adaptation. The impact of the new channel on voice capacity of the system is designed to be minimal because the F-PDCH utilizes resources that are not consumed by real-time users.

This paper addresses the problem of dynamic resource allocation in a multiservice direct-sequence code-division multiple-access (DS-CDMA) wireless network supporting real-time (RT) and nonreal-time (NRT) communication services. For RT users, a simple transmission power allocation strategy is assumed that maximizes the amount of capacity available to NRT users without violating quality of service requirements of RT users. For NRT users, a joint transmission power and spreading gain (transmission rate) allocation strategy, obtained via the solution of a constrained optimization problem, is provided. The solution maximizes the aggregate NRT throughput, subject to peak transmission power constraints and the capacity constraint imposed by RT users. The optimization problem is solved in a closed form, and the resulting resource allocation strategy is simple to implement as a hybrid CDMA/time-division multiple-access strategy. Numerical results are presented showing that the optimal resource allocation strategy can offer substantial performance gains over other conventional resource allocation strategies for DS-CDMA networks.

In this paper, we consider a direct-sequence code division multiple access (DS-CDMA) network consisting of a single radio access point and a collection of wireless terminals. The network offers two classes of service: class-1 (real-time) and class-2 (reliable). We are interested in studying the effect of dynamic spreading gain control (SGC) on the dynamics of multiple access interference (MAI), spectral efficiency, and the quality of service (QoS) experienced by each service class. We first consider a time-slotted system in which class-2 terminals operate in a random access fashion. We show that under optimal (throughput maximizing) dynamic SGC: (1) the optimal retransmission probability is equal to one, and (2) the optimal spreading gain increases linearly, or equivalently, the transmission rate decreases inverse linearly, as the MAI level increases. We then model the system as a continuous-time finite-source queueing system with processor sharing, and obtain an explicit (closed-form) expression for the stationary distribution of the number of active class-1 and class-2 terminals, that is, the MAI level. This distribution is used to derive expressions for various QoS measures and define a capacity or admissible region. The results obtained by simulation and analysis are in extremely close agreement. This work contributes to a better understanding of the relationships between QoS, multiple access interference, and allocation of radio resources in DS-CDMA networks.

With the purpose of reducing energy consumption and increasing network connectivity, the cooperative communication (CC) technique has been adopted for topology control. In previous studies, the concept of transmit diversity, which adds partial signals using a maximum ratio combiner, had only been considered and never fully exploited for receiver diversity. In this paper, we introduce a novel topology control algorithm that uses a receiver diversity. Compared with existing topology control algorithms, proposed scheme shows significant improvements in connectivity, computational complexity, and average power consumption per communication link.

In this paper, we analyze the coexistence between the International Mobile Telecommunications (IMT) system and the digital television (DTV) system in the 700MHz band. The 700MHz band is now called the “digital dividend” and is expected to be allocated to IMT services. This plan could cause mutual interference between existing broadcasting and the IMT services. The members in the Asia-Pacific Telecommunity Wireless Group are currently discussing the coexistence issues associated with the 700MHz band. In order to allocate this band to the IMT services without harming the DTV system, coexistence problems should be solved. This paper presents the simulation methodology for analyzing the mutual interference between the IMT and DTV system and provides the results of the performance degradation of the two systems.

In this paper, we consider the discrete memoryless user relaying channel (DMURC) in which a user-relay switches its operational mode symbol-by-symbol. In particular, we obtain upper and lower bounds on the channel capacity for the general DMURC and then show that these the upper and lower bounds coincide for degraded DMURC. It is also shown that the capacity of the degraded DMURC can be achieved using two separate codebooks corresponding to the two UR states. While the UR is assumed to switch states symbol-by-symbol, the results in this paper is the same as when the UR switches states packet-by-packet.

This paper focuses on a downlink beamforming problem in the cognitive radio~(CR) communication system where primary users~ (PU) coexist with secondary users~(SU). It is assumed that the SU transmitter has multiple antennas and transmits data to another SU's single-antenna receiver using the beamforming technique. By properly designing a beamforming vector, SU can maximize its channel gain while maintaining an interference with PU below a predefined level. In order to construct an optimal beamforming vector, the SU transmitter requires knowledge of the downlink channel information of both PU and SU receivers sent on the feedback channel. However, it is impractical to assume that the transmitter has the perfect channel state information~(CSI) considering the tremendous feedback overhead. One way to tackle this feedback overhead problem is to use a finite number of feedback bits indicating the index of a predefined codeword in the codebook. We analyze interference to the PU receiver and propose an algorithm to design a beamforming vector considering an error attributed to the partial CSI. The simulation shows that the analysis is quite accurate and that the beamforming vector, designed according to the proposed algorithm, keeps interference to PU below a predefined level while taking into account the error owing to the partial CSI. By using the proposed scheme, the CR system can become more robust against errors attributed to the partial CSI.

This paper considers the object tracking problem in three dimensional (3-D) space when the azimuth and elevation of the object are available from the passive acoustic sensor. The particle filtering technique can be directly applied to estimate the 3-D object location, but we propose to decompose the 3-D particle filter into the three planes" particle filters, which are individually designed for the 2-D bearings-only tracking problems. 2-D bearing information is derived from the azimuth and elevation of the object to be used for the 2-D particle filter. Two estimates of three planes" particle filters are selected based on the characterization of the acoustic sensor operation in a noisy environment. The Cramer-Rao Lower Bound of the proposed 2-D particle filter-based algorithm is derived and compared against the algorithm that is based on the direct 3-D particle filter.

This paper analyzes the system-level performance of the long term evolution (LTE)/LTE-Advanced (LTE-A). LTE/LTE-A has been considered to be a promising next generation communication system. It is proposed to ITU-R to be acknowledged as an IMT-Advanced technology. The performance of candidate technology proposals for IMT-Advanced should be evaluated to see if it satisfies the predefined minimum requirement of ITU-R. Note that ITU-R provides a report on evaluation guidelines, assumptions and minimum requirements, and it is strongly recommended that the guidelines and assumptions are followed when evaluating performance. This article summarizes the simulation methodology based on ITU-R guidelines and investigates the key technology, Multi-User MIMO (MU-MIMO), of LTE/LTE-A for IMT-Advanced. Simulation shows that LTE/LTE-A with the advanced MU-MIMO feature achieves performance above the ITU-R requirements, which cannot be achieved with Single-User MIMO (SU-MIMO).

We consider a queuing model with applications to electric vehicle (EV) charging systems in smart grids. We adopt a scheme where Electric Service Company (ESCo) broadcasts one bit signal to consumers indicating on-peak periods for the grid. EVs randomly suspend/resume charging based on the signal. To model the dynamics of the population of EVs we analyze an M/M/∞ queue with random interruptions, and propose estimates using time-scale decomposition. Using the estimates we show how ESCo can optimally adjust the indicator signal so as to minimize the mean number of charging EVs during the actual on-peak periods. Next we consider the case where EVs respond to the signal based on the individual loads. Simulation results show that performance is improved if the EVs carrying higher loads are less sensitive to the on-peak indicator signal.

An approach for dynamic object association and identification is proposed for heterogeneous sensor network consisting of visual and identification sensors. Visual sensors track objects by a 2D localization, and identification sensors (i.e., RFID system, fingerprint, or iris recognition system) are incorporated into the system for object identification. This paper illustrates the feasibility and effectiveness of information association between the position of objects estimated by visual sensors and their simultaneous registration of multiple objects. The proposed approach utilizes the object dynamics of entering and leaving the coverage of identification sensors, where the location information of identification sensors and objects is available. We investigate necessary association conditions using set operations where the sets are defined by the dynamics of the objects. The coverage of identification sensor is approximately modeled by the maximum sensing coverage for a simple association strategy. The effect of the discrepancy between the actual and the approximated coverage is addressed in terms of the association performance. We also present a coverage adjustment scheme using the object dynamics for the association stability. Finally, the proposed method is evaluated with a realistic scenario. The simulation results demonstrate the stability of the proposed method against nonideal phenomena such as false detection, false tracking, and inaccurate coverage model.

Object tracking by an acoustic sensor based on particle filtering is extended for the tracking of multiple objects. In order to overcome the inherent limitation of the acoustic sensor for the simultaneous multiple object tracking, support from the visual sensor is considered. Cooperation from the visual sensor, however, is better to be minimized, as the visual sensor's operation requires much higher computational resources than the acoustic sensor-based estimation, especially when the visual sensor is not dedicated to object tracking and deployed for other applications. The acoustic sensor mainly tracks multiple objects, and the visual sensor supports the tracking task only when the acoustic sensor has a difficulty. Several techniques based on particle filtering are used for multiple object tracking by the acoustic sensor, and the limitations of the acoustic sensor are discussed to identify the need for the visual sensor cooperation. Performance of the triggering-based cooperation by the two visual sensors is evaluated and compared with a periodic cooperation in a real environment.

In this paper. we consider an admission control algorithm for cellular networks. It is based on direct/dynamic monitoring of the QoS performances -- the delay tail of the admitted users. The main purpose of the direct monitoring of QoS performances is to guarantee the required QoS provision more precisely. The system delay tail is effectively computed by the proposed delay tail estimation algorithm. With the estimated delay tails, each base station determines the admission or rejection for a new user to the system. By doing so, the admission control algorithm becomes more robust against time-varying fading channel environment. Simulation results in OFDMA cellular system shows that the proposed algorithm can provide substantial capacity gains in offering QoS. We also use a general Neyman-Pearson-like framework in evaluating various admission control mechanisms.

In this paper, we consider the frequency reuse issue in the downlink of a multi-cell OFDMA system. We first implement the static frequency reuse scheme in the OFDMA sub-carrier assignment over the multi-cell system in order to control the inter-cell interference. Then, we add the random access sub-band to adopt the dynamic frequency reuse. The main purpose of introducing the random access sub-band is to improve the fairness of the system. In order to efficiently share the random access sub-band over the multi-cell sectors, the sector load information is considered. We assume that there is only a minimal coordination between the sectors so the central network controller provides only the access probabilities to each cell. With these probabilities, the sectors transmit the data on the random access channel. By doing so, the usage of the random access sub-band is randomized, and the fairness across the sector is provided by controlling the probabilities. Simulation results show that the proposed random access scheme achieve a performance improvement in the cell-edge user throughput. Index Terms—OFDMA, Multi-cell Scheduling, Frequency Reuse Factor

This paper revisits an optimal rate and power allocation problem to maximize throughput in uplink CDMA single-cell packet data communications. First, we show that the widely-accepted belief that an optimally selected rate always keeps a constant value of the resulting bit energy to the interference plus noise power spectral density ratio is not true in most practical CDMA packet transmission environments, where the packet size varies in proportion to the rate. Then, we derive the rate-dependent optimal bit energy-to-interference-noise power spectral density ratio, based on which we convert the original joint optimization problem of rate and power to an equivalent but simple power allocation problem. Finally, we derive an optimal power allocation strategy by applying the convex optimization theory. Through two instructive examples, we show that the optimality of the well-known bang bang power control, that is, each user (except at most one user) should either transmit his data at the maximum allowed power level or at the minimum required power level meeting the SINR requirement in order to maximize the system throughput, may or may not be true depending on the incorporated channel coding scheme.

The optimal resource allocation policy is studied in this paper, for nonreal-time users in CDMA reverse link. The resource allocation policy of interest includes channel coding, spreading gain control and power allocation under the conventional receiver operation-multiuser detection technique is not considered. The constraints in the optimization include peak transmit power of the mobile station, total received power at the base station and QoS in the form of minimum SINR for each user. The coding and spreading gain control can be separated from the power allocation strategy. Our results show that the optimal power allocation policy depends on the objective function: to maximize the sum of throughput from each user, a greedy policy is optimal where the good users (mobile stations with good radio conditions) transmit with full power, bad users (mobile stations with poor radio conditions) barely achieve their QoS and there is at most one user in-between; on the other hand, to maximize the product of throughput from each user, a fair policy is optimal where the bad users transmit with full power and the good users transmit with powers to reach a common received power level. The fairness of the optimal policy in the latter case makes QoS constraint unnecessary. Furthermore, we have found a unified approach in deriving these optimal policies. This approach can also be applied to other power allocation problems in CDMA reverse link. We also present numerical results on the channel capacity under both objectives and the effect of QoS constraint.

A novel forward link supervision algorithm applicable to power controlled CDMA systems is presented. This new algorithm relies upon the quality of the dedicated power control commands and is therefore compatible with systems that offer packet data service without an assigned dedicated Walsh code channel such as that found in commercial systems denned by IS-2000 Rev C. The algorithm is analyzed both analytically and with simulations. The conclusion from these analyzes show that the proposed forward link supervision algorithm does not affect the call quality, minimizes the impact on the reverse link capacity from unreliable power control commands and leads to call termination only if necessary.

The information-theoretic sum capacity of reverse link CDMA systems is investigated in this paper. As the reverse link CDMA systems are interference-limited, for given channel and noise conditions, the information-theoretic system capacity can be achieved by optimally managing the interference from mobile stations. Optimal interference management means optimal allocation of the transmit powers of the mobile stations. The exhaustive search of the optimal power allocation policy that maximizes the aggregate system capacity, requires O(N/sup M/) computations, where M is the number of the mobile station in the system and N is the granularity of the transmit power of a mobile station. In this paper, we prove that for a single cell, the number of computations to find the optimal power allocation solution can be reduced to O(NM), without sacrificing the optimality. We also show that an upper and a lower bound can be computed with O(M) computations, and the bounds are tight for small signal to noise ratio.

In this paper, we consider a DS-CDMA mobile network supporting real-time and non-real-time services. We study how the delay tolerance of non-real-time traffic can be exploited by allowing both transmission power control and variable spreading gain (transmission rate) control. Two control mechanisms adapt the received energy per bit to the current channel conditions and efficiently manage the multiple access interference so as to optimize performance. We provide the jointly optimal power and spreading gain allocation strategy of non-real-time sources. Our strategy maximizes non-real-time throughput subject to constraints on peak transmission power and protects QoS of real-time-services. We show that under the optimal strategy, the optimal spreading gains are inverse linear in the signal to interference plus noise ratio (SINR), and transmission power is allocated to the non-real-time sources in decreasing order of channel gain according to a greedy control strategy. We also present numerical results comparing the throughput and delay performance of the optimal strategy with other common strategies; the optimal strategy can offer substantial performance gains.

We consider a direct-sequence code division multiple access (DS-CDMA) network consisting of a single base station and a collection of mobile wireless terminals. There are two classes of traffic: voice and data. We provide a spectrally efficient multiple access protocol based on the dynamic control of the spreading gain of the data terminals. We also obtain expressions for key quality of service (QOS) metrics in terms of the number of active voice and data terminals. This work contributes to a better understanding of the relationships between the QOS, number of active terminals, and the allocation of radio resources in DS-CDMA networks.

In this paper, we consider a time-slotted DS-SSMA network consisting of a single radio access point and a finite number of mobile wireless terminals. The terminals generate "bursty" packet data and transmit in a random access fashion over a common broadband channel to the access point using different spreading codes. As in narrowband ALOHA systems, the performance of random access spread spectrum networks can be severely hampered due to saturation effects caused by inherent bistable behavior. We study the affect of dynamic spreading gain control on the stability and throughput properties of the network. We provide an optimal algorithm and establish a necessary and sufficient condition under which the algorithm eliminates bistability. If the condition holds, then the resulting operating point is the best possible; otherwise, the two resulting stability points are, in some sense, the best possible. In either case, the algorithm achieves high throughput.

We study the radio resource allocation problem of distributed joint transmission power control and spreading gain allocation in a DS-CDMA mobile data network. The network consists of K base stations and M wireless data users. The data streams generated by the users are treated as best-effort traffic, in the sense that there are no pre-specified constraints on the quality of the radio channels. We are interested in designing a distributed algorithm that achieves maximal (or near-maximal in some reasonable sense) aggregate throughput, subject to peak power constraints. We provide an algorithm where base stations coordinate in a distributed fashion to control the powers and spreading gains of the users, and show that it converges to a Nash equilibrium point. In general, there may be multiple equilibrium points; however, certain structural properties of the throughput expression can be exploited to significantly trim the search space and induce an ordering on the users in each cell. The numerical results indicate that with these modifications, the algorithm frequently converges in just a few iterations to the throughput maximizing (globally optimal) power and spreading gain allocation.