This paper describes an evolution and standardization trends of the wireless channel modeling activities towards IMT-Advanced. After a background survey on various channel modeling approaches is introduced, two well-known multiple-input-multiple-output (MIMO) channel models for cellular systems, namely, the 3GPP/3GPP2 Spatial Channel Model (SCM) and the IMT-Advanced MIMO Channel Model (IMT-Adv MCM) are compared, and their main similarities are pointed out. The performance of MIMO systems is greatly influenced by the spatial-temporal correlation properties of the underlying MIMO channels. Here, we investigate the spatial-temporal correlation characteristics of the 3GPP/3GPP2 SCM and the IMT-Adv MCM in term of their spatial multiplexing and spatial diversity gains. The main goals of this paper are to summarize the current state of the art, as well as to point out the gaps in the wireless channel modeling works, and thus hopefully to stimulate research in these areas.

Recently, frequency-domain equalization (FDE) has been attracting much attention as a way to improve single-carrier (SC) signal transmission in a frequency-selective wireless channel. Since the SC signal spectrum is spread over the entire signal bandwidth, FDE can take advantage of channel frequency-selectivity and achieve the frequency diversity gain. SC with FDE is a promising wireless signal transmission technique. In this article, we review the pioneering research done on SC with FDE. The principles of simple one-tap FDE, channel estimation, and residual inter-symbol interference (ISI) cancellation are presented. Multi-input/multi-output (MIMO) is an important technique to improve the transmission performance. Some of the studies on MIMO/SC with FDE are introduced.

The IEEE 802.16e standard specifies the sleep mode and the idle mode of a mobile station (MS) for power saving. In this paper, to reduce the energy consumption of the MS, we employ the sleep mode while the MS is on-session, and the idle mode while it is off-session. Under the assumption that the time duration from the end of a session to the arrival of a new downlink session request follows an exponential distribution of the mean and that arrivals of messages during an on-session follow a Poisson process with rate λ, we analyze the awake mode period and the sleep mode period by using the busy period analysis of the M/G/1 queue, and then we derive the total mean length of an on-session which consists of a geometric number of awake mode periods and sleep mode periods. Since the sum of an on-session and an off-session constitutes a cycle, we can express the average power consumption in terms of the mean lengths of an awake mode period, a sleep mode period and an idle mode period. The average power consumption indicates how much the MS can save energy by employing the sleep mode and the idle mode. We also derive the Laplace Stieltjes transform (and the mean) of the queueing delay of messages to examine a tradeoff between the power consumption and the delay of messages. Analytical results, which are shown to be well-matched by simulations, address that our employment of the sleep mode and the idle mode provides a considerable reduction in the energy consumption of the MS.

The Ethernet passive optical network (EPON), which is one of the PON technologies for realizing FTTx (Fiber-To-The-Curb/Home/Office), is a low-cost and high-speed solution to the bottleneck problem that occurs between a backbone network and end users. The EPON is compatible with existing customer devices that are equipped with an Ethernet card. To effectively control frame transmission from optical network units (ONUs) to an optical line termination (OLT), the EPON can use a multi-point control protocol (MPCP) with control functions in addition to the media access control (MAC) protocol function. In this paper, we propose a two-phase cycle dynamic bandwidth allocation (TCDBA) algorithm to increase the channel utilization on the uplink by allowing frame transmissions during computation periods, and combine the TCDBA algorithm with the queue management schemes performed within each ONU, in order to effectively support differentiated services. Additionally, we perform simulations to validate the effectiveness of the proposed algorithm. The results show that the proposed TCDBA algorithm improves the maximum throughput, average transmission delay, and average volume of frames discarded, compared with the existing algorithms. Furthermore, the proposed TCDBA algorithm is able to support differentiated quality of services (QoS).

Multimedia traffic on the Internet is rapidly increasing with the advent of broadband networks. However, the Best-Effort (BE) service used with Internet Protocol (IP) networking was never intended to guarantee Quality of Service (QoS) for each user. Therefore, the realization of QoS guarantees has become a very important issue. Previously, we have proposed a queue management scheme, called Dual Metrics Fair Queuing (DMFQ), to improve fairness and to guarantee QoS. DMFQ improves fairness and throughput by considering the amount of instantaneous and historical network resources consumed per flow. In addition, DMFQ has characteristics of high speed and high scalability because it is hardware oriented. However, DMFQ may be unable to adapt to network fluctuations, given that it has static setup parameters. Moreover, DMFQ is unable to support a multiclass environment. In this paper, we propose a new buffer management scheme based on DMFQ that can adapt flexibly to network conditions and can provide classified services. The proposed scheme stabilizes buffer utilization within a fixed range by controlling the buffer threshold, which affects the calculated packet discard probability. Moreover, by applying the proposed scheme to Differentiated Services (DiffServ), we achieve prioritized buffer management.

Recently several weighted clustering algorithms have been proposed, however, to the best of our knowledge; there is none that propagates weights to other nodes without weight message for leader election, normalizes node parameters and considers neighboring node parameters to calculate node weights. In this paper, we propose an Energy Efficient and Stable Weight Based Clustering (EE-SWBC) algorithm that elects cluster heads without sending any additional weight message. It propagates node parameters to its neighbors through neighbor discovery message (HELLO Message) and stores these parameters in neighborhood list. Each node normalizes parameters and efficiently calculates its own weight and the weights of neighboring nodes from that neighborhood table using Grey Decision Method (GDM). GDM finds the ideal solution (best node parameters in neighborhood list) and calculates node weights in comparison to the ideal solution. The node(s) with maximum weight (parameters closer to the ideal solution) are elected as cluster heads. In result, EE-SWBC fairly selects potential nodes with parameters closer to ideal solution with less overhead. Different performance metrics of EE-SWBC and Distributed Weighted Clustering Algorithm (DWCA) are compared through simulations. The simulation results show that EE-SWBC maintains fewer average numbers of stable clusters with minimum overhead, less energy consumption and fewer changes in cluster structure within network compared to DWCA.

Recently, SCTP is attracting attention to support mobility in the Internet because it does not require additional equipment such as the Home Agent of Mobile IP. This paper focuses on an SCTP fast handover mechanism using a single interface because it is assumed that small mobile devices have a single interface per communication medium such as IEEE802.11b due to hardware limitations. The proposed mechanism called SCTPmx employs a cross layer control information exchange system called LIES to predict handover. LIES was originally designed to achieve network layer fast handover and then it was extended by adding the network layer primitives for efficient interaction among the link layer, the network layer, and the transport layer. Prior to handover, SCTPmx can generate a new address that will be used after handover and can execute duplicate address detection of IPv6. SCTPmx can suppress the delay caused by channel scanning at the link layer by employing selective background scanning mechanism which allows to continue data communication during channel scanning. In addition, SCTPmx can notify the correspondent node of the new address before handover. SCTPmx was implemented on FreeBSD. SCTPmx achieved better than 25 times lower handover latency (100 msec) and 2 times higher throughput than previous proposals.

Orthogonal multi-carrier direct sequence code division multiple access (orthogonal MC DS-CDMA) is a combination of time-domain spreading and orthogonal frequency division multiplexing (OFDM). In orthogonal MC DS-CDMA, the frequency diversity gain can be obtained by applying frequency-domain equalization (FDE) based on minimum mean square error (MMSE) criterion to a block of OFDM symbols and can improve the bit error rate (BER) performance in a severe frequency-selective fading channel. FDE requires an accurate estimate of the channel gain. The channel gain can be estimated by removing the pilot modulation in the frequency domain. In this paper, we propose a pilot-assisted channel estimation suitable for orthogonal MC DS-CDMA with FDE and evaluate, by computer simulation, the BER performance in a frequency-selective Rayleigh fading channel.

Frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion can provide a better bit error rate (BER) performance than rake combining. However, the residual inter-chip interference (ICI) is produced after MMSE-FDE and this degrades the BER performance. Recently, we showed that frequency-domain ICI cancellation can bring the BER performance close to the theoretical lower bound. To further improve the BER performance, transmit antenna diversity technique is effective. Cyclic delay transmit diversity (CDTD) can increase the number of equivalent paths and hence achieve a large frequency diversity gain. Space-time transmit diversity (STTD) can obtain antenna diversity gain due to the space-time coding and achieve a better BER performance than CDTD. Objective of this paper is to show that the BER performance degradation of CDTD is mainly due to the residual ICI and that the introduction of ICI cancellation gives almost the same BER performance as STTD. This study provides a very important result that CDTD has a great advantage of providing a higher throughput than STTD. This is confirmed by computer simulation. The computer simulation results show that CDTD can achieve higher throughput than STTD when ICI cancellation is introduced.

In this paper, we focus on resource allocation schemes for minimizing the energy consumption of subscriber stations (SSs) in uplink flows of the IEEE 802.16 OFDMA systems. The resource allocation schemes assign subcarriers, powers, and data rates to each SS based on the measured signal to noise ratio (SNR) of the uplink channel and predefined modulation and coding scheme as system parameters. Previous research efforts to optimize resource allocation focus on the rate and throughput maximizations, and develop suboptimal heuristic algorithms. However, this paper intends to reduce the energy consumption of SSs by considering the relationship between energy efficiency and resource allocation. In order to clearly formulate the relationship, we use the Multiple Choice Knapsack (MCK) problem, which is proved to be an NP-hard problem. We propose two heuristic schemes to solve the NP-hard problem, which adaptively use the modulation and coding scheme, defined in the IEEE 802.16 OFDMA systems to minimize the required transmission power of each SS. Our simulation results show that the proposed schemes can reduce the energy consumption by up to 53% compared to the channel state information (CSI) scheme, which determines the modulation and coding level only considering the channel state information.

This paper proposes a blind image-band interference canceller that enables heterodyne receivers with only a single receiver chain to demodulate signals in any frequency band. In this paper, such a receiver is called "multimode/multiband heterodyne receiver." If multimode/multiband receivers are desired to receive signals with carrier frequency ranging from several MHz to GHz, then, such receivers are not allowed to have a narrow band RF-BPF (Radio Frequency Band Pass Filter) at the RF front end. However, although heterodyne receivers have been applied to wireless systems due to their high performance, it is known that without an RF-BPF heterodyne receivers suffer from severe image-band interference. Therefore, a blind image-band interference canceller is proposed in this paper to mitigate the image-band interference. Moreover, a novel algorithm based on the CM (Constant Modulus) criterion is proposed to carry out the cancellation. Performance of the blind image-band interference canceller is theoretically analyzed and the performance of the proposed canceller is verified by computer simulation. As a result, it is shown that the blind image-band interference canceller achieves superior performance even in the presence of strong image-band interference, for example, CIR=-40 dB. In summary, the proposed canceller makes it possible for the receiver with the single receiver chain to achieve multimode/multiband communications with high quality.

The predictability of network traffic is an important and widely studied topic because it can lead to the solutions to get more efficient dynamic bandwidth allocation, admission control, congestion control and better performance wireless networks. Support vector machine (SVM) is a novel type of learning machine based on statistical learning theory, can solve small-sample learning problems. The work presented in this paper aims to examine the feasibility of applying SVM to predict actual WLAN traffic. We study one-step-ahead prediction and multi-step-ahead prediction without any assumption on the statistical property of actual WLAN traffic. We also evaluate the performance of different prediction models such as ARIMA, FARIMA, artificial neural network, and wavelet-based model using three actual WLAN traffic. The results show that the SVM-based model for predicting WLAN traffic is reasonable and feasible and has the best performance among the above mentioned prediction models.

In this paper, a method of the signal subspace interpolation to constructing a continuous fingerprint database for radio localization is proposed. When using the fingerprint technique, enhancing the accuracy of location estimation requires very fine spatial resolution of the database, which entails much time in collecting the data to build up the database. Interpolated signal subspace is presented to achieve a fine spatial resolution of the fingerprint database. The angle of arrival (AOA) and the measured signal subspace at known locations are needed to obtain the interpolated signal subspaces. The effectiveness of this method is verified by an outdoor experiment and the estimated location using this method was compared with those using the geometrically calculated fingerprint and the measured signal subspace fingerprint techniques.

The attenuation effect of the walls of a building on the electromagnetic (EM) field generated by an indoor power line communication (PLC) system is numerically investigated using the finite integration (FI) method. In particular, we focus on the frequency range 2-6 MHz, for which the attenuation effect has not yet been sufficiently analyzed. We model a single, finite-sized wall instead of an entire house, to focus on the dependence of the EM field on the wall structure and also reduce the computational resources required. The EM field strength is evaluated at many points on a view plane 10 m from the wall model, and the results are statistically processed to determine the attenuation effect of the wall. We show that the leakage of an EM field at 2-6 MHz is suppressed by about 30 dB by a reinforced concrete wall. We also show that the main contributor to the attenuation effect is the rebar in the wall. We then investigate the relation between the attenuation effect of a single-wall model and that of a house model. The results show that the attenuation effect of a house model is almost the same as that of a 15-m-wall model. We conclude that the use of a single-wall model instead of a house model is effective in determining the attenuation of the EM leakage. This simple structure reduces analytic space, time, and memory in the evaluation of the dependence on the wall structure of the EM leakage from indoor PLC systems.

This paper presents a new cycle time synchronization method to transmit isochronous multimedia data by real time in IEEE 1394 over a UWB (ultra wide-band) network. The 1394 TA recommended two methods for the cycle time synchronization. The first method must use two consecutive beacon signals to calculate a drift correction, while the second one eliminates this dependency with minor algorithm changes. As experimental results, the second method achieves 21% performance improvement over the first one. The receipt of two consecutive beacons every time is hard due to the noise in a wireless channel. In addition, this paper provides the procedure of cycle time synchronization, as well as the transaction between 1394 protocol adaptation layer and IEEE 802.15.3 media access layer. The proposed synchronization technique will contribute to transfer isochronous data at IEEE 1394 over UWB audio/visual appliances such as camcorder, HDTV, etc.

Kiyomoto-Fukushima-Tanaka proposed a perfectly anonymous attribute authentication scheme that realizes unidentifiable and untraceable authentication with offline revocation checking. The Kiyomoto-Fukushima-Tanaka scheme uses a self-blindable certificate that a user can change randomly. Thus, the certificate is modified for each authentication and the authentication scheme has the unidentifiable property and the untraceable property. However, in this letter, we show that the Kiyomoto-Fukushima-Tanaka scheme is insecure against the impersonation attack.

A coordinate plane representation of the resource requirements of digital modulation methods is presented, and an overall resource efficiency measure is proposed. This measure can be used for the comparison of digital modulation methods and the evaluation of an emerging modulation technique. Several typical digital modulation methods are compared based on this measure to show its validity.

We investigate numerically the applicability of photonic crystal fiber (PCF) with a uniform air hole structure as a wide-band transmission medium. We show that accumulated dispersion over the PCF can be reduced effectively by optimizing the index profile of dispersion compensating fiber (DCF). We also show that a bandwidth of more than 300 nm will be available for 40 Gbit/s NRZ transmission by using the PCF as a transmission medium instead of conventional 1.3 µm zero-dispersion single-mode fiber (SMF).

In this paper, we study an opportunistic scheduling and adaptive modulation scheme for a wireless network with an XOR network coding scheme, which results in a cross-layer problem for MAC and physical layers. A similar problem was studied in [2] which considered an idealized system with the Shannon capacity. They showed that it may not be optimal for a relay node to encode all possible native packets and there exists the optimal subset of native packets that depends on the channel condition at the receiver node of each native packet. In this paper, we consider a more realistic model than that of [2] with a practical modulation scheme such as M-PSK. We show that the optimal policy is to encode native as many native packets as possible in the network coding group into a coded packet regardless of the channel condition at the receiver node for each native packet, which is a different conclusion from that of [2]. However, we show that adaptive modulation, in which the constellation size of a coded packet is adjusted based on the channel condition of each receiver node, provides a higher throughput than fixed modulation, in which its constellation size is always fixed regardless of the channel condition at each receiver node.

It is well known that the performance of CDMA systems may degrade in the presence of spreading code mismatch. The diagonal loading multiple constrained minimum variance (DL-MCMV) approaches have been proposed to deal with the mismatch problem. However, they still cannot improve the robust capability efficiently due to the spreading code mismatch. In this letter, a detector based on the variable DL technique is presented that offers more robust capabilities than the MCMV and DL-MCMV detectors. Computer simulation results are provided that illustrate the effectiveness of the proposed detector.

A semi-distributed resource allocation scheme based on multihop equilibrium is proposed for OFDM-relay networks. This method aims to reduce the amount of feedback information from the relay nodes (RNs). Moreover, it utilizes radio resource by striking an efficient balance between the capacities of the BS-RN link and RN-MS link. Simulation results show that the proposed semi-distributed scheme achieves good performances in terms of throughputs and fraction of satisfied users.

For integrated WLAN/cellular networks, we propose an energy-efficient vertical handover mechanism that both improves the energy efficiency of the mobile nodes and reduces the WLAN frame overhead.

The beamforming weights which can suppress the interfering signal toward out-of-cell mobile stations in downlink are designed for a time division duplexing based OFDMA system when the channel information is not perfect. The derived beamforming weights do not improve the average SINR performance monotonously with the increased transmit SNR if the inverse of the transmit SNR is used as the regularization factor of the beamforming weights and the channel information obtained by the BS to design the BF weights is not perfect. Therefore, we suggest a simple scheme to select the regularization factor. The proposed beamforming weights improve the performance monotonously with the increased transmit SNR and achieve near-optimal performance. The performance achieved by applying the beamforming weights used in uplink to downlink beamforming is also investigated.

In this letter, a recursive ICI cancellation technique for cooperative space-time block coded orthogonal frequency division multiplexing (STBC-OFDM) systems is proposed to mitigate the intercarrier interference (ICI) caused by multiple carrier frequency offsets (CFOs) in cooperative transmission. The proposed technique is shown to mitigate the noise enhancement effect on the STBC-OFDM signals caused by multiple CFOs, and to be effective in reducing ICI especially when the system has a large FFT size and multiple CFOs.

The cognitive radio technique promises to manage and allocate the scarce radio spectrum in the highly varying and disparate modern environments. This paper considers a cognitive radio scenario composed of two queues for the primary (licensed) users and cognitive (unlicensed) users. According to the Markov process, the system state equations are derived and an optimization model for the system is proposed. Next, the system performance is evaluated by calculations which show the rationality of our system model. Furthermore, discussions among different parameters for the system are presented based on the experimental results.

The distributed antenna system (DAS) offers significant power savings but only if the antennas are properly located. In this letter, we convert antenna location optimization to the codebook design problem. For the widely studied circular-layout DAS with uniform user distribution, we derive closed-form expressions for antenna locations that yield near-optimal performance. For more general user distribution and antenna topology, the codebook design algorithms can provide numerical optimization results with acceptable performance and low complexity.

This letter presents beam tilting characteristics of a slot antenna element with reactance loading. It is found that the beam tilt is obtained by controlling aperture electric field distributions with a loaded reactance on the slot. A large beam tilt angle is obtained when an inductive reactance element is loaded.

This paper presents a field penetration characteristic, into a metallic wall with a narrow slot, due to a nearby dipole source. Coupled integral equations are derived and solved by applying Galerkin's method of moments (MoM) for calculating the penetrating electric field. It is shown that the 26 dB attenuation level field penetration into the narrow slot occurs at the dipole source position of much more than about 0.6 λ separation distance along the lateral direction from the slot center. It is also found that the 30 dB attenuation levels field penetration appear at the observation positions of much more than about 0.5 λ along the direction of the slot length and about 1.07 λ separation distance along the direction of the slot width from the slot center.

In order to incorporate the reader/writers (RWs) into mobile electronic devices, miniaturization and flexibility are required. To meet these requirements, we fabricate an ultra-small RW with multiple contactless interfaces by mounting main unit circuits inside the antenna coil and using flexible multi-layer circuit board.

Research of the shortest path problem in time-dependent networks has important practical value. An improved pheromone update strategy suitable for time-dependent networks was proposed. Under this strategy, the residual pheromone of each road can accurately reflect the change of weighted value of each road. An improved selection strategy between adjacent cities was used to compute the cities' transfer probabilities, as a result, the amount of calculation is greatly reduced. To avoid the algorithm converging to the local optimal solution, the ant colony algorithm was combined with genetic algorithm. In this way, the solutions after each traversal were used as the initial species to carry out single-point crossover. An improved ant colony algorithm for the shortest path problem in time-dependent networks based on these improved strategies was presented. The simulation results show that the improved algorithm has greater probability to get the global optimal solution, and the convergence rate of algorithm is better than traditional ant colony algorithm.