Top PDF Performance analysis of equalized OFDM systems in Rayleigh fading

This paper presents a systematic approach for analyzing the bit-error probability (BEP) of equalized OFDM signals in Rayleigh fading. Closed-form expressions for BEP performance of various signal constellations [phase-shift keying (PSK), differ- ential phase-shift keying (DPSSK), quaternary phase-shift keying (QPSK)] are provided for receivers that use a linear pilot-assisted channel estimate. We also derive the optimal linear channel esti- mates that yield the minimum BEP and show that some previous known results are special cases of our general formulae. The results obtained here can be applied to evaluate the performance of equalized single-carrier narrowband systems as well.

Published online: 3 February 2010 © Springer Science+Business Media, LLC. 2010 Abstract This paper presents the root-mean-squared tracking error performance analysis of a class of coherent digital delay-locked loops for multicode direct sequence spread spec- trum signals in bandlimited correlated Rayleigh fading channels. In the transmit side, multiple independent PSK-modulated data streams in the in-phase and qudrature phase branches are spread by short mutually orthogonal codes before being further complex spread by a long complex PN code. We assume that the system employs a pilot code channel to assist the receiver’s synchronization and channel estimation. The proposed code tracking loop incorpo- rates the pilot-aided channel estimator and derives the timing error from all short-code-spread subchannels. Our analysis takes into account the effects of imperfect channel estimate, corre- lated frequency selective Rayleigh fading and band-limiting. Numerical results are presented to quantify the impact of the resulting multipath interference within the same code channel and amongst different code channels.

Fig. 3 shows the analytical error floors corresponding to a set of spreading factors L = {31, 63, 127, 255, 511, 1023} for the case of K = 5. The SISO RBSC system and the 2ISO RBSC system using the SML detector are treated as the baseline systems, and only their theoretical BERs are illustrated. One should note that for the TU120 channel model, the number of previous symbols resulting in ISI is N = 1 if L ∈ L. However, for the HT120 channel model, we have 1) N = 3 if L = 31; 2) N = 2 if L = 63; and 3) N = 1 if L ∈ {127, 255, 511, 1023}. As discussed in Section IV, it is the MPI, MUI, and crosstalk that cause the error floors. For the DBSC systems, the JML detector, being robust to the crosstalk, obtains the best performance, while the SML detector, ignoring the crosstalk, obtains the worst performance. Moreover, increasing L has three impacts on the system performance. First, the power of the total interference

complexity and/or a more complicated performance analysis. Two approaches, namely direct and flow-graph approaches, have been applied extensively for analyzing the performance of an acquisition system, probability mass function (PMF), and/or moments of the acquisition time [3], [8]–[10]. Theoretically, these two methods are only applicable to the AWGN channels because the homogeneous Markov chain modeling of the ac- quisition process, a fundamental assumption of these methods, is no longer valid for time-variant multipath fading channels due to the channel memory incurred by fading; an analysis without considering the correlations due to fading may only be considered as an approximation. Unfortunately, as to be shown, the analysis error due to no consideration on the channel correlations can be very large, especially for the acquisition system based on passive correlators. A more accurate analysis for fading channels is yet to be found.

II. System model We consider a point-to-point MIMO system with M transmit antennas and M receive antennas. In the mean- while, we adopt OFDM modulation with total N T sub- carriers and let a group of adjacent N T /N subcarriers form a subchannel. The total bandwidth of each subchan- nel is assumed to be smaller than the channel coherent bandwidth. Figure 1 shows the considered structure of the OFDM-based spatial multiplexing systems, where M N independent data streams are multiplexed in M trans- mit antennas and N subchannels. The transmit power is uniformly split to M transmit antennas. It is assumed that the length of the cyclic prefix (CP) in the OFDM system is greater than the length of the discrete-time baseband channel impulse response so that the frequency- selective fading channel indeed decouples into a set of parallel frequency-flat fading channels [19]. With x n and y n denoting the M ×1 transmit and receive signal vectors, respectively, we can write

ABSTRACT The OFDM (orthogonal frequency division multiplexing) signaling is one kind of "Multi-Carrier" technology, which can slow down delayed transmission especially for operating at frequency non-selective fading channels. Therefore, it gains quite large profit making a study of executing efficiency at different frequency non-selective fading channels. The OFDM system has become the most popular choice of transmission modulation in the new wireless communication field. Hence, in this article utilize a method of OFDM modulation to explore the statistical characteristic of distributions of Rayleigh、Ricean、Weibull while working in fading channel.

V. C ONCLUSION Different transmitter-based preprocessing methods are jointly inves- tigated with spreading pattern optimization and multiuser scheduling for the 2-D OFDM-CDMA forward-link systems from an information- theoretic viewpoint. The ergodic sum data rate serves as the perfor- mance index for performance comparisons under the assumption of perfect CSI. Examples are given to illustrate the important issue of spreading pattern optimization. ZF-MWF performs the best among the preprocessing methods that were investigated, including ZF and the MMSE. Moreover, as expected, multiuser scheduling gives a significant performance improvement.

VI. C ONCLUSIONS In this paper, we review the NSD and its three special cases, namely, the CR, DR, and VR. Based on the estimator-detector structures, a hierarchical interpretation of the NSD and its spe- cial cases are also presented. Then the NSD and its special cases are applied to the differential OFDM systems with diversity re- ception. Moreover, assuming sufficient CP, we provide a simple closed-form BER expression for differential OFDM systems employing the CR with diversity reception in the time-varying multipath Rayleigh fading channels. Numerical results have revealed that, with multi-antenna diversity reception, the per- formance of the CR is improved significantly. However, when few receive antennas are available, the implementation of the DR or VR is necessary for achieving better and satisfactory performance.

ABSTRACT In this paper the system performance of OFDM (orthogonal frequency division multiplexing) with the cases of MRC (maximal ratio combining) and dual branch SC (selective combining) diversities over correlated-Gamma distributed and correlated-Weibull fading, respectively, are investigated. Since the reason of an alternative expression of the Q-function is adopted for deriving the results of average BER (bit-error rate) of the OFDM system, the obtained formulas are not only calculated much simpler but the conducting of numerical analysis is also arrived at easily and accurate. It is valuable to claim that the system performance of the OFDM system is definitely dominated by the propagation environments, which is decided by the fading parameters both of the Nakagami-m and Weibull distributed, of the transmission of the radio systems. Furthermore, both of the conditions of equal and unequal signal intensities at the output of SC diversities are adopted as the scenarios for the discussion of OFDM systems.

To significantly reduce the complexity and achieve high performance at the same time, this paper proposes three efficient non-coherent cell ID detection methods based on a new optimization metric and its simplifications. These new methods are not only suitable for IEEE 802.16 and IEEE 802.16e systems but also suitable for other preamble-based OFDM systems. By combining a preamble matching process and a multiplication-free smoothing scheme, the proposed techniques achieve better performances than the existing tech- niques in multipath Rayleigh fading channels. Based on our preliminary work [1], which introduces a basic concept of smoothing for cell ID detection, this paper generalizes the design concept and provide a statistical characterization for the proposed methods. Moreover, for further reducing the complexity, we introduce the decimation factor 𝑑 into the conventional and proposed methods as shown in the section of simulation results. With the decimation, all the methods can achieve lower computational complexities. For a sys- tem suffering the burst error, reducing the complexity by decimation may be better than reducing the complexity by directly shortening the correlation length in [22]. Therefore, by appropriately choosing the value of decimation factor 𝑑, the proposed methods can achieve the similar complexities as [22], but with better system performances.

Publisher Item Identifier S 0090-6778(02)03505-5. function. The 2-D function takes into account the correlations of the fading process in time and frequency domains. We can also use a one-dimensional (1-D) function to model the channel variation on each subchannel. Our method is simpler than those of previous LMMSE proposals. Every symbol in each subchannel needs less than four complex multiplications in the equalization process, and no information about the channel correlation and noise power level is needed. Furthermore, although the LS method is more sensitive to noise than the LMMSE method, our second-stage algorithm is very effective in reducing the LS estimation error.

Abstract— With the increasing number of wireless network in- frastructure deployment and the popularity of portable computing devices, more and more internet users are experiencing ubiquitous mobility using both these computing devices and the wireless net- works to access the Internet. Therefore, it is necessary to study the loss behavior of the multimedia applications such as Web Brows- ing, VoIP, Teleconferencing, over wireless networks. This paper applies a matrix-analytic approach to analyze the loss probability of multimedia services over a Rayleigh fading channel. Due to the versatility of Discrete-time Markovian arrival process (D-BMAP) as an input process, the queuing model of the Burst-error commu- nication channel is a D-BMAP/D/1/K queue, where K is the buffer capacity.

The effectiveness of erasure side information generated by Vterhi's ratio threshold test (RTT) decision for frequency-hopped multiple access @"MA) systems with M-ary [r]

Because of the unique features of the RB, by using proper network architecture and using advanced modulation formats [3]–[5], RB-induced signal degradation can be mitigated. This is particularly true for PON using centralized carrier distribution. Dense wavelength-division-multiplexed (DWDM) PONs employing centralized optical carrier distribution and wavelength-insensitive (colorless) reflective optical networking units (RONUs) are attractive since the wavelength referencing

The main contribution of this paper is that for better characterizations of synchronization errors under a practical communication environment, that is, in doubly-selective fading channels, we analyze joint e ffects of the mentioned three major synchronization errors, without the assumption of small STO. Another contribution is that compact forms can be derived from our work to gain further insights on the synchronization error e ffects. To this end, we first analyze the signal model of the combined synchronization errors in time-selective and frequency-selective fading channels by extending the works in [1–15]. Next, based on this model, the theoretical SINR is formulated. The derived SINR can be exploited to obtain all possible combinations of syn- chronization errors that meet the required SINR constraint, knowing that the allowable synchronization errors could help design suitable synchronization algorithms and shorten the design cycle. To gain further insights, some compact

Based on the foregoing results, the determination of the shap- ing filter for the second stage reduces to the choice of a suit- able operating value for α. For this, we do not have a theoreti- cally optimal formula, but only some rules of thumb. Experience shows that underestimation of α would not cause significant en- hancement of total MSE when the true α is large enough. In contrast, if the true α is small, then overestimation of it would cause great increase of the MSE. This phenomenon is heuris- tically reasonable, because (true) α is defined to be equal to σ n 2 /σ 2 e . Assuming a smaller value for α than its true value is tantamount to assuming a less converged state, which may re- sult in some slowdown in the convergence speed but would not likely cause stability problems. On the other hand, assuming a larger value for α than its true value means being over-optimistic on the convergence status, which would more likely cause per- formance degradation. Therefore, we choose to use a reasonably small value in the place of α. By experiment, we find that a suit- able range of its values is 0.5–2, with unity being a good choice.

Transmit Equal Gain Precoding in Rayleigh Fading Channels Shang-Ho Tsai Abstract—Precoding with limited feedback information can achieve satisfactory performance while the amount of feedback information is kept small. In this paper, we analyze the theoretical performance of equal gain precoder and find that its performance is at most 1.049 dB worse than the optimal precoder no matter how the number of transmit antennas increases. Moreover, we analyze the performance degradation of the equal gain precoder due to scalar quantization theoretically. The result shows that 2–3 bits per transmit antenna (excluding the first antenna) can achieve 0.5–0.25-dB performance gap compared with the same scheme without quantization. Furthermore, we found that the equal gain precoder in general can achieve comparable performance with the Grassmannian precoder in the same moderate feedback bits. Simulation results are provided to corroborate the theoretical results.

II. OFDM S YSTEM AND S IGNAL M ODELS In the following discussion, all the quantities indexed with l belong to the lth symbol. A simplified OFDM system model is shown in Fig. 1, where X l, k / ˜ X l, k is the transmitted/received frequency-domain data at the kth subcarrier, x l,n is the trans- mitted time-domain data after the IFFT, and ˜ x l,n  is the received time-domain data, where −N G n  < N , N is the number of subcarriers, and N G is the CP length. 1/T S is the sampling fre- quency, ε f is the CFO (normalized by the subcarrier spacing), f c is the CF, n  Δ is the estimated STO, and ε  f is the estimated CFO. On the transmitter side, N complex data symbols are modulated onto N subcarriers by using the IFFT. The last N G IFFT output samples are copied to form the CP that is inserted at the beginning of each OFDM symbol. By inserting the CP, a guard interval is created so that ISI can be avoided and the orthogonality among subcarriers can be sustained. The

ABSTRACT In this paper, the impact of the correlation on the performance of multiple-cell DS-CDMA cellular systems over correlated fading channels is investigated. A new closed-form formula for the joint probability density function (joint pdf) of the diversity combiner with arbitrary correlation coefficients in terms of the generalized Laguere polynomial and the new expressions of average bit-error rate (BER) for the DS-CDMA system are given in this paper. The results demonstrate that the BER is significantly dependent on the correlation characteristic of diversity branching for multiple-cell environments.

An analytic expression for the bit error probability upper bounds of rate-| convolutional codes in conjunction with QPSK modulation and maximum-likelihood Viterbi decod- ing on the fully[r]