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Communications Letters, IEEE

Issue 5 • Date May 2006

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Displaying Results 1 - 25 of 37
  • IEEE Communications Letters - May 2006, Vol. 10, No. 5

    Page(s): 01
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    Freely Available from IEEE
  • Low complexity MAP detection using approximate LLR for CDMA iterative receivers

    Page(s): 321 - 323
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (221 KB) |  | HTML iconHTML  

    In this letter, we approximate the log-likelihood ratio (LLR) to find computationally efficient detectors for the iterative receiver in code division multiple access (CDMA) systems. For approximation, a Taylor series of the LLR is considered. One of the well-known detectors is rederived using a first order approximation, while a new detector is found by a second order approximation. View full abstract»

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  • Forgery attacks on digital signature schemes without using one-way hash and message redundancy

    Page(s): 324 - 325
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (72 KB) |  | HTML iconHTML  

    Chang and Chang proposed a new digital signature scheme, and claimed the scheme can resist the forgery attack without using one-way hash function and any redundancy padding. This claim is very interesting to all designers, because conventionally a one-way hash function is required to resist the attacks. This article shows an existential forgery attack on the scheme, and shows that the scheme would still be insecure even if a secure one-way function were adopted in the scheme. View full abstract»

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  • Upper bound on one-coincidence sequences of odd length with distance constraints in frequency-hopping spread-spectrum systems

    Page(s): 326 - 328
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (160 KB) |  | HTML iconHTML  

    We deal with one-coincidence sequences for the frequency-hopping CDMA systems. We derive an upper bound on the number of one-coincidence sequences of odd length where the distances between all adjacent frequency indices are required to be greater than a specified distance value. It is shown that there exist infinitely many cases in which our bound is tighter than the conventional bound. View full abstract»

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  • Implications of third generation wireless standards for the design of superconducting transmit filters

    Page(s): 329 - 331
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (258 KB) |  | HTML iconHTML  

    Superconducting technology enables high-Q transmit filters for wireless base stations. However, superconducting filters are inherently nonlinear devices that cause signal distortion and spectral broadening. Third generation wireless CDMA2000 and WCDMA standards constrain the modulation accuracy and out-of-band emissions. The out-of-band emission requirements are shown to be the limiting factors that control the filter and resonator designs. View full abstract»

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  • Spatially correlated MIMO channel-generation via virtual channel representation

    Page(s): 332 - 334
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB) |  | HTML iconHTML  

    This paper presents a new spatially correlated Rayleigh fading channel generation technique for multiple-input-multiple-output (MIMO) systems via recently proposed virtual channel representation (VCR). In contrast to the traditional production correlated channel generation, the new VCR approach generates correlated channel via two dimensional discrete Fourier transform (DFT). This work extends the theoretical correlation coefficient results from single-input-multiple-output (SIMO) to MIMO channels. In addition, theoretically we show that the currently used production method is a special case of the new VCR technique, since the former considers only local scatterers, but the latter considers non-local scatterers as well. Hence, this work leads to the conclusion that VCR is a more general channel model compared with 2-D production-form. View full abstract»

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  • A novel performance analysis model for an IEEE 802.11 wireless LAN

    Page(s): 335 - 337
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (203 KB) |  | HTML iconHTML  

    This letter presents a novel analytic model that accurately evaluates the performance of a single-hop IEEE 802.11 wireless LAN (WLAN). By using a closed queuing network, we model an IEEE 802.11 WLAN system that consists of a fixed number of stations and derive the saturated throughput of the IEEE 802.11 distributed coordination function (DCF). The ns-2 simulation results show that our new analysis model is very accurate in evaluating the performance of the IEEE 802.11 DCF. View full abstract»

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  • A new technique for reducing MAC address overheads in sensor networks

    Page(s): 338 - 340
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (172 KB) |  | HTML iconHTML  

    In sensor networks, the size of the medium access control (MAC) address is prohibitively expensive when one considers the small payload and the cost of transmitting one bit. We address this problem by proposing a technique that encodes L-bits of the payload with a key derived from MAC addresses. We show how the decoding process removes the need for MAC addresses in packets. View full abstract»

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  • On the network utility optimal allocation of radio resources in WCDMA systems

    Page(s): 341 - 343
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (166 KB) |  | HTML iconHTML  

    We discuss an optimization framework for radio resource allocation in a WCDMA system supporting elastic traffic. In particular, we assume the users' preferences as driven by utility functions depending on the assigned transmission rate, and the network capacity constraints as related to interference and power limitations. In this framework, we perform the constrained instantaneous network utility maximization through a logarithmic barrier method. The obtained results are compared and discussed. View full abstract»

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  • A performance analysis framework for limited feedback beamforming in correlated fading

    Page(s): 344 - 346
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (203 KB) |  | HTML iconHTML  

    Limited or finite rate, feedback is an efficient way to implement beamforming in multiple antenna systems using frequency division duplexing. Unfortunately, closed-form performance analysis of limited feedback beamforming has not been investigated. This paper provides an analytical framework for the correlated limited feedback beamforming problem by treating selection of the beamforming vector from the codebook as a multibranch selection problem. View full abstract»

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  • Frequency-domain correlative coding for MIMO-OFDM systems over fast fading channels

    Page(s): 347 - 349
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (220 KB) |  | HTML iconHTML  

    Multiple-input multiple-output (MEMO) antennas combined with orthogonal frequency division multiplexing (OFDM) are very attractive for high-data-rate communications. However, MEMO-OFDM systems are very vulnerable to time-selective fading as channel time-variation destroys the orthogonality among subchannels, causing inter-carrier interference (ICI). In this letter, we apply frequency-domain correlative coding in MEMO-OFDM systems over frequency-selective, fast-fading channels to mitigate ICI. We derive the analytical expression of the carrier-to-interference ratio (CIR) to quantify the impact of time-selective fading and demonstrate the effectiveness of correlative coding in mitigating ICI in MEMO-OFDM systems. View full abstract»

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  • Data-aided channel estimation for turbo-PIC MIMO detectors

    Page(s): 350 - 352
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB) |  | HTML iconHTML  

    We consider data-aided channel estimation for multiple input multiple output (MIMO) systems when iterative parallel interference cancellation (PIC) is performed for signal detection. We compare some data-aided channel estimation methods based on expectation maximization (EM) algorithm or on hard estimated transmit symbols. In particular, we propose a modified EM-based approach and show that when few iterations are to be performed, it provides considerable performance improvement. View full abstract»

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  • On the performance analysis of digital communications over generalized-K fading channels

    Page(s): 353 - 355
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (300 KB) |  | HTML iconHTML  

    The performance of digital communication systems over generalized-K (KG) fading channels is analyzed and evaluated. Novel closed form expressions for the SNR statistics, the average Shannon's channel capacity and the bit error rate (BER) are derived. These expressions are used to study important performance criteria such as the outage performance, the average capacity and the BER for a great variety of modulation formats in KG fading channels. The proposed mathematical analysis is accompanied with various performance evaluation results, which demonstrate the usefulness of the proposed approach. View full abstract»

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  • MIMO-OFDM with insufficient cyclic prefix

    Page(s): 356 - 358
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (252 KB) |  | HTML iconHTML  

    For orthogonal frequency division multiplexing (OFDM), cyclic prefix (CP) should be longer than the length of channel impulse response, resulting in a loss of bandwidth efficiency. In this letter, the CP reconstruction (CPR) technique is first applied to a multi-input multi-output (MIMO)-OFDM system with insufficient CP. The intercarrier interference (ICI) from multiple transmit antennas is so large for MIMO system that it can not be sufficiently suppressed with the conventional CPR procedure used in single-input single-output (SISO) system. A new minimum mean-square error (MMSE) equalization and ordering process is proposed for MIMO system to suppress the ICI during the CPR procedure. By applying the proposed CPR algorithm to MIMO-OFDM system, we can obtain both the benefits of multiplexing gain and spectral efficiency gain. View full abstract»

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  • Correction to "Comments on 'On the connectivity in finite ad hoc networks'"

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    The probability of connectivity of a one-dimensional finite ad hoc network was derived by Desai and Manjunath, and further analyzed by Gore. In this letter, we point out a discrepancy, thus corroborating the original result. However, it provides the exact interpretation of the recursion and derives the probability of connectivity of a one-dimensional finite sensor network. View full abstract»

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  • Bandwidth and region division for broadband multi-cell networks

    Page(s): 360 - 362
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (300 KB) |  | HTML iconHTML  

    A cell planning technique termed BRD (bandwidth and region division) is presented for overcoming interference, maintaining QoS (quality of service) and improving channel capacity over OFDM (orthogonal frequency division multiplexing)-based broadband cellular networks. Through an optimal combination of sectorization and zero padding, bandwidth and region division is achieved that minimizes the outage probability for forward-link cell planning. In order to verify the effectiveness of the proposed algorithm, a Monte Carlo simulation is performed over multi-cell environments. View full abstract»

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  • On the minimum pseudo-codewords of LDPC codes

    Page(s): 363 - 365
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (144 KB) |  | HTML iconHTML  

    In this letter, we study the minimum pseudo-codewords of low-density parity-check (LDPC) codes under linear programming (LP) decoding. We show that a lower bound of Chaichanavong and Siegel on the pseudo-weight of a pseudo-codeword is tight if and only if this pseudo-codeword is a real multiple of a codeword. Using this result we further show that for some LDPC codes, e.g., Euclidean plane and projective plane LDPC codes, there are no other minimum pseudo-codewords except the real multiples of minimum codewords. View full abstract»

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  • A 2×2 antennas ultra-wideband system with biorthogonal pulse position modulation

    Page(s): 366 - 368
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB) |  | HTML iconHTML  

    The Golden code is a 2×2 space-time code that achieves the best known performance with all constellations carved from Z[i]. In this letter, we present the construction of a new coding scheme for 2M-ary biorthogonal pulse position modulations (BPPM) with M≥4. The proposed code satisfies all of the construction constraints of the Golden code and it has the additional advantage of being totally real making it suitable for low cost carrier-less ultra-wideband terminals. Namely, this totally real construction achieves full rate and full diversity with the best known coding gain and without any shaping losses for 2M-BPPM with M≥4. View full abstract»

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  • Linear time encoding of cycle GF(2p) codes through graph analysis

    Page(s): 369 - 371
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (222 KB) |  | HTML iconHTML  

    In this letter, we present a linear-complexity encoding algorithm for any cycle GF(2P) code CE(G,H). We just need to investigate the case where G is a nontrivial connected graph. If G is a tree, the only codeword is the all-zero word. If G is not a tree, first, we show that through graph analysis H can be transformed into an equivalent block-diagonal upper-triangular form simply by permuting the rows and columns of H; then, we show that whether H is full row-rank or not, the code can be encoded in linear time. View full abstract»

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  • A class of irregular LDPC codes with low error floor and low encoding complexity

    Page(s): 372 - 374
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (179 KB) |  | HTML iconHTML  

    In this letter, we propose a class of irregular structured low-density parity-check (LDPC) codes with low error floor and low encoding complexity by designing the parity check matrix in a triangular plus dual-diagonal form. The proposed irregular codes clearly lower the error floor and dramatically improve the performance in the waterfall region of error-rate curves. Being characterized by linear encoding complexity, the encoders of the proposed codes attain throughputs over 10 Gbit/s. View full abstract»

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  • Improved decoding of LDPC coded modulations

    Page(s): 375 - 377
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (244 KB) |  | HTML iconHTML  

    A coded modulation belief propagation (CMBP) decoder is proposed for decoding LDPC codes with multilevel modulations. The decoder takes into account statistical dependencies among bits originating in the same symbol, providing better performance than the marginal BP (MBP) decoder. Asymptotically it converges to MAP decoding. The CMBP decoder is based on a single-level coding (SLC) scheme and does not suffer from practical disadvantages of multi-level coding (MLC) schemes. Furthermore, the CMBP decoder can close the capacity gap of the bit interleaved coded modulation (BICM) SLC scheme. The BICM capacity gap increases when the modulation size increases and in scenarios where gray mapping is not possible. View full abstract»

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  • A decision feedback based scheme for Slepian-Wolf coding of sources with hidden Markov correlation

    Page(s): 378 - 380
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (217 KB) |  | HTML iconHTML  

    We consider the problem of compression of two memoryless binary sources, the correlation between which is defined by a hidden Markov model (HMM). We propose a decision feedback (DF) based scheme which when used with low density parity check codes results in compression close to the Slepian-Wolf limit. View full abstract»

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  • On the stopping distance of finite geometry LDPC codes

    Page(s): 381 - 383
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (132 KB) |  | HTML iconHTML  

    In this letter, the stopping sets and stopping distance of finite geometry LDPC (FG-LDPC) codes are studied. It is known that FG-LDPC codes are majority-logic decodable and a lower bound on the minimum distance can be thus obtained. It is shown in this letter that this lower bound on the minimum distance of FG-LDPC codes is also a lower bound on the stopping distance of FG-LDPC codes, which implies that FG-LDPC codes have considerably large stopping distance. This may explain in one respect why some FG-LDPC codes perform well with iterative decoding in spite of having many cycles of length 4 in their Tanner graphs. View full abstract»

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  • Modeling conditional FER for hybrid ARQ

    Page(s): 384 - 386
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (187 KB) |  | HTML iconHTML  

    This letter investigates the conditional frame error rate (FER) of hybrid automatic repeat request (HARQ) retransmission conditioned on its previous erroneous transmission. For simplification, it is called 'conditional FER' in this letter. On the basis of theoretical analysis, this letter validates the necessity of modeling conditional FER in wireless communication systems with HARQ and proposes a low-complexity implementation method. Simulation results prove the method's accuracy. View full abstract»

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  • A pair of asymmetric weighting receivers and polyphase codes for efficient aperiodic correlations

    Page(s): 387 - 389
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (495 KB) |  | HTML iconHTML  

    Sequences with low autocorrelation levels are highly desirable in digital communication. Conventional sidelobe reduction techniques have suffered from performance degradations in range resolutions and signal-to-noise ratio (SNR) gains. In this paper we propose a way to synthesize amplitude weight correlators for polyphase codes. These weighted codes generate sidelobes that are lower than those found in Barker codes. The sidelobe level is kept uniformly flat over all time delays while the range resolution loss is prevented. Unlike the Barker codes, the proposed technique is not limited by the code length. The technique is easy to implement and incurs a minimal SNR loss. View full abstract»

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Aristotle University of Thessaloniki
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