# IEEE Communications Letters

Published by Institute of Electrical and Electronics Engineers

Print ISSN: 1089-7798

Published by Institute of Electrical and Electronics Engineers

Print ISSN: 1089-7798

Publications

We develop improved algorithms to construct good low-density parity-check codes that approach the Shannon limit very closely. For rate 1/2, the best code found has a threshold within 0.0045 dB of the Shannon limit of the binary-input additive white Gaussian noise channel. Simulation results with a somewhat simpler code show that we can achieve within 0.04 dB of the Shannon limit at a bit error rate of 10/sup -6/ using a block length of 10/sup 7/.

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The authors show that the Shannon capacity limit for the additive white Gaussian noise (AWGN) channel can be approached within 0.27 dB at a bit error rate (BER) of 10/sup -5/ by applying long but simple Hamming codes as component codes to an iterative turbo-decoding scheme. In general, the complexity of soft-in/soft-out decoding of binary block codes is rather high. However, the application of a neurocomputer in combination with a parallelization of the decoding rule facilitates an implementation of the decoding algorithm in the logarithmic domain which requires only matrix additions and multiplications. But the storage requirement might still be quite high depending on the interleavers used.

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Power line communication technology is one of the most tractable home-networking technologies, because existing power line facilities can be utilized for data communications without deploying any new physical links. Although HomePlug 1.0, the power line communication standard, has undergone field trials and simulations, its analytic model and performance was not presented. In this letter, we analyze the performance of HomePlug 1.0 in terms of saturation throughput.

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Cooperative diversity schemes significantly improve the performance of wireless networks by transmitting the same information through several nodes. The amplify-and-forward (AF) relaying method is one of the most attractive cooperative diversity schemes due to its low complexity. Selection AF relaying has recently been proven to achieve the same diversity order as and lower outage probability than all-participate relays. In this letter, we present an asymptotic analysis of the symbol error rates of a selection AF network, and compare it with the conventional all-participate scheme

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An exact intuitive geometric infinite double series for the average symbol error probability of 128-cross-QAM and 512-cross-QAM in additive white Gaussian noise is derived. New simple and precise approximations for the average symbol error probabilities are also derived.

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We describe computer simulation and laboratory performance results of a real-time two-element adaptive antenna array testbed for the uplink of a 1.9-GHz IS-136 PCS base station. Our simulations and real-time experimental results with a channel emulator show less than a 1-dB implementation loss as compared to theoretical results for the noise-only case. With interference, at low fading rates the implementation loss to is only a few decibels. However, the performance degrades with increasing fading rate, such that the adaptive array performance is similar to maximal ratio combining at 60-m/h fading rates (179 Hz at 1.9 GHz).

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In this paper, we study the connected dominating set (CDS) problem in disk graphs. The CDS problem has a significant impact on an efficient design of routing protocols in wireless networks. This problem has been studied extensively in unit disk graphs, in which each node has the same transmission range. However, in wireless ad hoc networks, the transmission ranges of all nodes are not necessary equal. In this paper, we introduce the CDS problem in disk graphs and present a constant approximation algorithm which can be implemented as a distributed algorithm.

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IEEE 1588 is a standard to synchronize independent clocks running on separate nodes of a distributed measurement and control system. In IP based cellular network, it is considered as a key technology to synchronize base stations. Especially, interests for the low-cost and very-small home cellular base station called the Femtocell is increasing, and it is connected to the cellular core network using an asymmetric communication link such as xDSL. However, the conventional IEEE 1588 synchronization algorithm assumes symmetrical links, and makes errors for asymmetric links for the calculation of the time difference between the master clock (a clock source) and the slave clock (a clock consumer). We propose an enhanced synchronization algorithm to calculate the asymmetric ratio of the communication link, and the proposed algorithm enhances an accuracy of the time synchronization.

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IEEE 1588 is a standard to synchronize independent clocks running on separate nodes of a distributed measurement and control system. In PTN (Packet Transport Network), it is considered as a key technology for supporting legacy TDM services and synchronizing 3G base stations. However, conventional IEEE 1588 synchronization algorithm assumes symmetrical links, and makes errors for asymmetric links for the calculation of the time difference between the master clock and the slave clock. We proposed an enhanced time synchronization method to calculate the time difference and the proposed method enhances an accuracy of the time synchronization.

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Although the result of Part II of Theorem 1 in Z.Q. Taha and X. Liu (2007) is correct, the proof is incorrect. A corrected proof is given in this letter.

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High peak-to-mean envelope power ratio has been a major issue in the implementation of orthogonal frequency division multiplexing systems in low cost application devices. In this letter, we construct code with low peak to mean envelope power ratio based on construction of STAR-16-QAM constellation as a scaled set sum of two QPSK constellations. The construction of Golay sequences based on STAR-16-QAM constellation is shown and upper bound for peak-to-mean envelope power ratio for OFDM is derived.

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In IEEE 802.16 networks, a bandwidth request-grant mechanism is used to accommodate various QoS requirements of heterogeneous traffic. However, it may not be effective for TCP flows since (a) there is no strict QoS requirement in TCP traffic; and (b) it is difficult to estimate the amount of required bandwidth due to dynamic changes of the sending rate. In this letter, we propose a new uplink scheduling scheme for best-effort TCP traffic in IEEE 802.16 networks. The proposed scheme does not need any bandwidth request process for allocation. Instead, it estimates the amount of bandwidth required for a flow based on its current sending rate. Through simulation, we show that the proposed scheme is effective to allocate bandwidth for TCP flows.

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New space-time codes for 4PSK constellations were designed via a modified determinant criterion at 2b/s/Hz and were shown to perform well under conditions of quasi-static flat fading. The transmit antennas used the same M-PSK complex modulator constellation M of unit average energy and exactly log 2 M bits transmitted during each multiple channel use. The equal eigen value criterion for L-transmit-antenna Rayleigh fading with perfect channel state information (CSI) was used for the numerical analysis.

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We design constellation labeling maps for bit-interleaved space-time coded modulation with iterative decoding (BI-STCM-ID) over Rayleigh block-fading channels using the Alamouti scheme and N<sub>r</sub> receive antennas. To achieve the largest asymptotic coding gain from the constellation labeling, we propose a new design criterion that maximizes the (-2N<sub>r</sub>)-th power mean of the squared Euclidean distances associated with all "error-free feedback" events in the constellation. Based on this power mean criterion, we show that the labeling optimization problem falls into the category of quadratic assignment problems. We propose two novel 16-QAM labeling maps that are particularly designed for N<sub>r</sub>=1 and N<sub>r</sub>=2, respectively. Numerical results show that both labeling maps achieve about 1 dB coding gain over the conventional 16-QAM modified set partitioning labeling.

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A tag-collision problem (or missed reads) in RFID system is the event that a reader cannot identify the tag if many tags respond to a reader at the same time. Recently, Choi et al. proposed a 16-bit random number query tree algorithm (RN16QTA) for RFID tag anti-collision by using a RN16 as the tags temporary ID. RN16QTA successfully reduce the time consumption for tag identification than the present identification implemented in EPC Class 1 Gen. 2. However, simulation results and the theoretical estimation imply that the length of RN16 is actually not enough in real environments to successfully identify tags. In this letter, we propose an effective RN16QTA (ERN16QTA) to really solve the tag collision in tags identification. Moreover, our new algorithm saves the responded bits.

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This paper evaluates a new RFID reservation MAC protocol that utilizes tree based collision avoidance. Performance evaluation is conducted for tag read latency and read efficiency as a function of link parameters defined in ISO/IEC 18000-6 Type C standard.

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The cdma2000 1xEV-DO standard has a distributed rate control on the reverse link. If a mobile has data to transmit, it determines the data rate of the next frame in response to a reverse activity bit broadcast by the base station. This paper proposes an analytical framework for the 1xEV-DO rate control by adopting the noise rise as the reverse traffic load, and by modeling the rate control as a discrete Markov process. We validate the proposed model through a simulation, in which 1xEV-DO reverse power control is applied to a Rayleigh fading channel. In addition, we illustrate the operation principle of the 1xEV-DO rate control based on the data rate distribution of mobiles.

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cdma2000 UEV-130 standard has a distributed rate control scheme on a reverse link. In this paper, we propose an adaptive rate control scheme based on the control of Rate Limit, which is a maximum possible data rate in the reverse link. From numerical and simulation results, it is shown that our proposed scheme achieves significant capacity gain in reverse link compared to 1xEV-D0 rate control scheme.

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The Home Phoneline Networking Alliance (HomePNA) 2.0 is an attractive proposition for home networking since it potentially allows transmission rates comparable to those of Ethernet, using existing installed telephone lines. This system adopts a CSMA/CD medium access control protocol with distributed fair priority queuing (DFPQ). We present a simple analytical model to compute the saturation throughput performance in the presence of a finite number of contending stations, which provides a guideline to the design of systems.

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Both mathematically and numerically, we prove that the hashing equation used to determine the second paging indicator bit of IS-2000 quick paging channel is not optimal. A new hashing equation is proposed that is more uniformly random, and thus improves the efficiency of the quick paging channel.

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We design an optimal linear precoder for a space-time coded system assuming knowledge of only the transmit antenna fading correlations. Assuming a flat fading channel and a maximum-likelihood receiver, we show that the linear precoder transmits power on the eigenmodes of the transmit antenna correlation matrix. The power allocation on the eigenmodes is a form of waterpouring policy. Simulation results are presented to show performance improvement on a space-time coded system.

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We consider the linear combination of two ISI free pulses, the raised cosine (RC) and the recently proposed better than raised cosine (BTRC). We determine their optimum combination using the distribution of timing error. The obtained pulses perform better than RC and BTRC for fixed as well as randomly distributed timing errors.

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In this letter, we extend the method that has been proposed in the literature for calculating the bit error probability of two-dimensional (2D) RAKE receivers in asynchronous direct sequence code-division multiple access (DS-CDMA) over flat, slow Rayleigh fading channels to the case of frequency-selective, slow Rayleigh fading channels. We also compute and plot the lower bound on the performance that can be achieved in the above system.

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Optical CDMA is proposed to implement a PON that supports downstream native optical multicasting. Common wavelengths within provisioned 2D codes may uniquely represent a multicast group. We introduce a simple architecture enabling native 2D-OCDMA multicasting without resorting to code tunability. We outline the associated code-provisioning problem and demonstrate clear SIR advantages compared to 2D-OCDMA.

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We solve optimal symbol dimensions for a recently introduced two-dimensional orthogonal frequency division multiplexing (2D OFDM) scheme with a two-dimensional cyclic prefix (2D CP). The 2D OFDM technique is shown to improve the rate of a wireless relaying system if the channel coherence time is at least nine times longer than the channel impulse response. Furthermore, feasibility and application scenarios of 2D OFDM are discussed using the parameters of terrestrial digital video broadcasting systems (DVB-T/H) as examples.

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We propose an efficient 2Ntimes2N MIMO detection algorithm where the transmit signals are grouped in pairs and separately coded using the standard Alamouti space-time code. At the receiver, one or more QR decompositions are performed and the upper triangular property of the R matrices so obtained is exploited in order to successively decode the transmitted symbols starting with those interference-free symbols corresponding to the last two rows and columns of R. Bit-error-rate simulation results, for a 4times4 MIMO system and a bandwidth efficiency of 8 bits/s/Hz, show that the proposed technique, while less complex than ordered MMSE V-BLAST, outperforms the latter by 2-6 dB at a BER of 10<sup>-4</sup>

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The Home Phoneline Networking Alliance (HomePNA) 3.0 technology is designed to provide high-speed backbones for home multimedia networks. This technology adopts a collision management protocol in an asynchronous medium access control (MAC) mode to reduce the number of collisions. In this letter, we present a simple analytical model to compute the saturation throughput performance of the collision management protocol, and compare the performance with that of HomePNA 2.0.

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Novel closed-form exact expressions for the average symbol error probability of 32-cross-QAM in an additive white Gaussian noise channel and in a slow, flat Nakagami fading channel with L-branch maximal ratio combining diversity are derived

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Two-factor authentication is favorable to securely identifying remote users in a communications network. Lately cryptographic camouflage was applied for the purpose by software-only techniques. However it can be vulnerable to impersonation attacks via interleaved sessions if a single server is compromised. This article brings to light such a hidden weak point and suggests a possible solution.

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Using Hamiltonian p-cycles, it can be shown that p-cycle design is able to reach the logical redundancy bound of 1/(d~-1) where d~ is the average node degree. We formulate two conditions on which the design is able to reach this bound if and only if Hamiltonian p-cycles are used.

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This paper presents 38-GHz wide-band point-to-multipoint measurement results from various weather events. 73963 measured power delay profiles indicate that multipath can occur due to the foliage and the reflection from wet surfaces during rain. The received signal strength during rain varies according to a Rician distribution with a K factor inversely proportional to the rain rate. The measured rain attenuation exceeds Crane's model prediction by several decibels. The results may aid in design of broadband millimeter-wave communication systems.

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This paper investigates the problem of location and velocity detection of a mobile agent using Received Signal Strength (RSS) measurements captured by geographically distributed seed nodes. With inherently nonlinear power measurements, we derive a powerful linear measurement scheme using an analytical measurement conversion technique which can readily be used with RSS measuring sensors. We also employ the concept of sensor fusion in conjunction for the case of redundant measurements to further enhance the estimation accuracy.

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The behavior and performance of a UMTS network are governed by a number of parameter settings that are configured by the network operator, e.g., timeouts. In this letter we show that the actual value of such parameters can be inferred by a conceptually simple set of end-to-end measurements, without any cooperation with the network operator. In principle, such information can be used by researchers to define realistic network scenarios, e.g., for their simulations. Moreover, it can be used by a malicious attacker to fine-tune a large scale attack against the radio access network, e.g., a paging attack.

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Loose coupling between 3G and WLAN ensures flexibility and openness. However, providing an ubiquitous mobile voice service in a loosely coupled 3G/WLAN network requires both packet-level and call-level quality of service (QoS) guarantees using soft vertical handoff (SVHO) and call admission control (CAC). In this paper, we evaluate the impact of both SVHO and WLAN mobility on call blocking and dropping probabilities rederived for the integrated network. For this purpose, we propose a new multi-region mobility model that accurately estimate these probabilities under a resource-efficient dynamic threshold SVHO compared to a standard static-threshold SVHO. Results show us that the resource-efficient SVHO blocks and drops much less voice calls than the static one when very low mean and high variability of multi-mode mobile station velocities are noticed. Therefore, resource-efficient SVHO implementations are highly recommended in these mobility environments.

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The authors study the feasibility of a real-time 3G UMTS terminal detector to be located in a restricted area. All idle terminals entering the restricted area are forced to emit signaling information which can be captured. The authors analyze the detector protocol settings and response time. They also determine the conditions it would impose on UMTS operators.

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Due to the traditional separation of radio and IP engineering in 3G cellular networks, the subscriber access-request rate from the RAN is usually a known parameter to radio engineers, whereas the corresponding authentication, authorization, and accounting (AAA) traffic rate generated by the network access server (NAS) in response to the RAN requests is unknown. To bridge this design gap, we analyze a typical NAS-AAA system architecture based on the RADIUS protocol, the de-facto protocol for authentication and billing adopted by the telecom industry. We present the first analytical model for the mean and the variance of the AAA signaling rate and verify it by simulations. The model results can help operators to configure their NASes with proper accounting-interim-interval values as a tradeoff between network cost and accounting reliability

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Although third generation cellular networks are being deployed in many countries, rigorous measurement studies from public networks have yet to be published. After extensive experimentation, we collect measurements from a commercial WCDMA 3G/UMTS network and observe that the goodput of the first of a series of back-to-back transfers is consistently below par. We compare these results with those obtained from an all-wired network and show that 3G signaling plays an important, albeit detrimental role in end-user goodput. Finally, we illustrate that near-nominal goodput is realizable for large payloads only.

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In this letter, we propose a flexible channel assignment scheme using preemption as an access method for integrated voice/data transmissions over common packet channel (CPCH) in 3GPP. We analyze the proposed scheme and compare the performance of the proposed scheme with the performance of the basic, channel monitoring, and channel assignment schemes in view of the voice packet dropping probability and the average delay of data packet.

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Realizing machine-to-machine (M2M) communications requires to construct and to manage scrupulous connections (logically and physically) from devices controllers to an enormous number of devices. By leveraging existing cellular infrastructures providing higher layers connections, the most challenging task is to efficiently manage massive accesses on the air interface. Consequently, in this letter, a massive access management (MAM) is proposed, which provides the most critical guarantees of quality-of-service (QoS), for devices. By deriving sufficient conditions of QoS guarantees, we show that the proposed MAM can effectively satisfy diverse QoS requirements, thus enabling the M2M communications over 3GPP scenarios.

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We consider WDM mesh networks with finite signal impairment threshold (SIT) and estimate the minimum requirement of 3R wavelength converters (3R-WCs) per node. We find that the marginal utility of 3R-WC diminishes rapidly and relatively small number of 3R-WCs is enough to enhance the network performance to that of a WDM network with infinite SIT and wavelength converters at all the channels per node.

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In the last years, a lot of attention has been devoted to both multi-antenna systems with space-time orthogonal block coding (STOBC) and ultra wideband (UWB) transceivers based on impulse-radio (IR) technologies. In this short contribution we anticipate the architecture of a novel transceiver merging both multi-antenna and pulse position modulation (PPM) IR-UWB techniques and then we test the performance in flat-faded application scenarios typical of emerging broadband 4G WLANs. Three main appealing features are retained by the sketched transceiver scheme. First, it allows to equip the UWB receiver with reliable estimates of the (possibly time-varying) underlying multiple-input multiple-output (MIMO) UWB without reducing the overall information throughput conveyed by the system. Second, the performance confirms that the proposed transceiver is able to achieve "full diversity" even at SNRs as low as 1.5-2 dB. As a consequence, the resulting BERs outperform those of current Single-Input Single-Output (SISO) IR-UWB transceivers over two orders of magnitude even at SNR's as low as 3-4 dB. Third, at target BER's below 10<sup>-2</sup> and radiated powers around 250 μW, the coverage ranges allowed by the proposed MIMO IR-UWB scheme typically outperform those of conventional SISO IR-UWB ones of about two orders of magnitude.

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This letter contains measured data and empirical models for 5.85-GHz radio propagation path loss in and around residential areas for the newly allocated National Information Infrastructure (NII) band in the U.S. Three homes and two stands of trees were studied for outdoor path loss, tree loss, and house penetration loss in a narrow-band measurement campaign that included 270 local area path loss measurements and over 276000 instantaneous power measurements. The data will aid the development of futuristic outdoor-to-indoor wireless unlicensed NII systems (in the U.S.) and HIPERLAN systems (in Europe) for home Internet access, telecommunications, and wireless local loops.

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IEEE 802.15.4 low-rate Wireless Personal Area Networks (WPAN) are expected to provide ubiquitous networking between small personal/home devices and sensors with low power consumption and low cost features. The technology employs special CSMA/CA to save power consumption for batterypowered small or portable WPAN devices. In this letter, we present a new model for the slotted CSMA/CA of IEEE 802.15.4 Medium Access Control (MAC) and evaluate its throughput limit in order to grasp the characteristics of IEEE 802.15.4 WPAN.

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Large path losses of millimeter waves restrain the acceptance of 60 GHz technology in future networks. Directional antennas can be exploited in 60 GHz networks to mitigate the detrimental impact of fading. Employing fully directional antennas complicates the neighbor discovery process where each sector must be probed individually to discover neighbors located in that sector. In random scanning strategy, nodes select to-be-scanned sector randomly. In this letter, we analyze the minimum number of random sector scanning attempts during neighbor discovery process to have a non-isolated network. We present an analytical model to study the isolation probability defined as probability of having at least one isolated node in the network. Based on the isolation probability, we derive the minimum number of sector scanning attempts in a 60 GHz ad hoc network with arbitrary number of nodes. Although 60 GHz directional network is studied, this analysis is applicable to any directional wireless network.

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This letter studies the performance of indoor wireless communication systems operating at 60 GHz with different polarization schemes. Circular polarization is known to reduce multipath effects in line-of-sight (LOS) environments in the 60 GHz band. We propose a modified channel model based on the IEEE 802.15.3c channel model to incorporate the polarization effects. We then use this model to evaluate the error performance of a wireless communication system that uses circular polarization. The results are compared with linear polarization for LOS environments.

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We demonstrate a moving extended cell concept that provides seamless communication with high end-user mobility in broadband 60 GHz Radio-over-Fiber networks. Mathematical and simulation-based performance analysis are presented, showing that this technique can guarantee seamless connectivity irrespective of the overlapping area between adjacent cells providing zero packet loss and call dropping probability values for up to 40m/sec mobile speeds.

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60GHz radio is a promising technology since it can offer multi-Gbps data rate. However, 60 GHz radio based transmission is easily disturbed by co-channel interference (CCI). In this letter, a novel analytical model is provided to investigate the performance of using synchronization (sync) frames to mitigate CCI. The performance improvement while using sync frames is demonstrated in terms of throughput and the guaranteed transmission distance.

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This letter considers the problem of designing efficient routing algorithms for the backward network of a bidirectional general shuffle-exchange network (BNBGSEN for short); switch elements in the network are of size k×k. It has been shown in (Z. Chen, et al., 2003) that the algorithm in (K. Padmanabham, 1991) can be used to obtain (as many as k) backward control tags for a source j to get to a destination i in a BNBGSEN. In this letter, we show that a BNBGSEN has a wonderful property: for each destination i, there are two backward control tags associated with it such that every source j can get to i by using one of the two tags. We use this property to derive an efficient tag-based routing algorithm.

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Terrestrial radio signals at frequencies above 70 GHz are vulnerable to atmospheric absorption by rain. In order to prevent traffic loss in radio network, caused by finite duration of rerouting algorithm convergence, protection method based on pre-calculated backup routes is proposed. Using two-dimensional rain cell model, a performance analysis is held out for different rain parameters in network with adaptive modulation/capacity links. It is shown that under influence of moderate rain intensity, a network protected by proposed method can have performance very close to that of a rerouted network.

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In wireless mobile ad hoc networks (MANETs), it is essential that all mobile hosts (MHs) are synchronized to a common clock to support the power-saving (PS) mechanism. Many protocols have been proposed for clock synchronization in IEEE 802.11 MANETs. However, it is practically impossible for any protocol to completely solve the asynchronism problem especially when connectivity is achieved by multi-hop communication or when a network could be temporarily disconnected. In this work, we propose a quorum-based mechanism, which includes a new structure of beacon intervals for MHs to detect potential asynchronous neighbors and an enhanced beacon transmission rule to assist clock synchronization protocols to discover asynchronous neighbors within bounded time. The proposed mechanism should be regarded as an enhancement to existing clock synchronization protocols. Our simulation results show that the mechanism can effectively relieve the clock asynchronism problem for IEEE 802.11 MANETs

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