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... Ranging process in IEEE 802. 16 system provides a number of functionalities, such as initial network entry, uplink synchronization, power adjustment, and system coordination. In further work [7], a novel ranging transmission power control algorithm which reduces the interference between MS-BS ranging and MS-RS ranging was discussed. ...
... Performance results and the comparison of computational complexity with traditional methods were also presented [15]. New ranging designs which enable multiuser diversity gain and facilitate new efficient low complexity algorithms for multiuser ranging signal detection, timing estimation, and power estimation were studied [16]. ...
... The probability of detection miss rate due to narrowband jamming in a Nakagami fading channel with EGC diversity is derived by combining (4) and (16). Hence, ...
Ranging is a process where the base station (BS) identifies a mobile station (MS) among many other MSs with the help of Ranging code set, which is unique to each MS. Also, an estimation process is made to find the transition time delay which is the difference between the time at which the MS sends some data and the time at which the BS receives data. In this paper, the effect caused by jamming on the Ranging process will be analyzed. Jamming destroys orthogonality/pseudo orthogonality of the Ranging code set which affects the estimation of the codes. This in turn affects parameters like detection miss rate. This paper also discusses the improvement in the Ranging process where diversity techniques like maximal ratio combining (MRC), selection combining (SC), and equal gain combining are used. These diversity techniques are used in various fading channel models like Rayleigh, Rician, and Nakagami. The analyses indicate that for a Rayleigh fading channel, the code word error rate (CER) decreases by two orders of magnitude for a SC case as compared to the no diversity case, and that CER reduces by three orders of magnitude for an Equal Gain/MRC case as compared to the no diversity case. Similar results are observed for Rician and Nakagami fading channels also.
... Other ranging detection approaches [85][86][87][124][125][126][127] were proposed to mitigate the MAI by specially designed ranging codes and modulation schemes. Because this study focuses on the detection algorithm, we confine ourselves to the more general contention based OFDMA ranging channel model, which is compliant to the IEEE 802.16 standard. ...
Orthogonal frequency-division multiplexing (OFDM) has been adopted by many broadband wireless communication systems for the simplicity of the receiver technique to support high data rates and user mobility. However, studies also show that the advantage of OFDM over the single-carrier modulation schemes could be substantially compromised by timing or frequency estimation errors at the receiver. In this thesis we investigate the synchronization problem for practical OFDM systems using a system model generalized from the IEEE 802.11 and IEEE 802.16 standards. For preamble based synchronization schemes, which are most common in the downlink of wireless communication systems, we propose a novel timing acquisition algorithm which minimizes false alarm probability and indirectly improves correct detection probability. We then introduce a universal fractional carrier frequency offset (CFO) estimator that outperforms conventional methods at low signal to noise ratio with lower complexity. More accurate timing and frequency estimates can be obtained by our proposed frequency-domain algorithms incorporating channel knowledge. We derive four joint frequency, timing, and channel estimators with different approximations, and then propose a hybrid integer CFO estimation scheme to provide flexible performance and complexity tradeoffs. When the exact channel delay profile is unknown at the receiver, we present a successive timing estimation algorithm to solve the timing ambiguity. Both analytical and simulation results are presented to confirm the performance of the proposed methods in various realistic channel conditions. ...
Initial ranging (IR) is a process of performing power adjustment, timing offset estimation, and synchronisation between the base station (BS) and all users. It plays a vital role in mobile WiMAX standard, which establishes a communication link between BS and ranging subscriber stations (RSSs). Since RSS is located far away from the BS and uplink signal is corrupted by noise, the IR process becomes inferior. Thus, the authors propose an improved dynamic threshold‐based IR method comprising three phases: (i) code detection phase, (ii) filtering phase, and (iii) parameter estimation phase. In the first two phases, the received signal is pre‐processed to eliminate noise and unselected codes from the codeset by employing adaptive filter and weight‐based code detection method. Then, the noise‐free signal is considered for the final phase, which improves accuracy. The iterative expectation maximisation algorithm is involved in the estimation of channel coefficient and timing offset. All possible active paths are detected by setting a dynamic threshold value for each channel by the enhanced dynamic threshold method. For all active channels, round trip delay, and power level are estimated by considering particular channel coefficient and timing offset. Extensive simulation of proposed work shows considerable improvements in performance.
In this study, a maximum likelihood distance estimation algorithm is proposed for a multi-carrier radar system to estimate the time delay of non-integer sampling intervals. Particularly, the equivalent relationship between time domain delay and frequency domain phase shift and the relationship between target delay and channel impulse response is used. The idea of maximum likelihood estimation is to find the estimation value that maximises the likelihood function. Therefore, the core idea of this algorithm is the peak search. First, channel estimation is performed on the sampled signal in frequency domain to obtain the channel impulse response. Second, phase compensation and peak search is done to estimate the target delay. Finally, for multiple estimation results, the authors statistic the probability density distribution of the target. In addition, they deduce the Cramer–Rao bound (CRB) of the variance of time delay estimation. The measurement accuracy of the algorithm that they proposed approaches the CRB in the high signal-to-noise regime.
In this paper, resource allocation for energy-efficient secure communication in an orthogonal frequency-division multiple-access (OFDMA) downlink network is studied. The considered problem is modeled as a nonconvex optimization problem that takes into account the sum-rate-dependent circuit power consumption, multiple-antenna eavesdropper, artificial noise generation, and different quality-of-service (QoS) requirements, including a minimum required secrecy sum rate and a maximum tolerable secrecy outage probability. The power, secrecy data rate, and subcarrier allocation policies are optimized for maximization of the energy efficiency of secure data transmission (bit/joule securely delivered to the users). The considered nonconvex optimization problem is transformed into a convex optimization problem by exploiting the properties of fractional programming, which results in an efficient iterative resource allocation algorithm. In each iteration, the transformed problem is solved by using dual decomposition. Simulation results illustrate that the proposed iterative resource allocation algorithm not only converges in a small number of iterations but maximizes the system energy efficiency and guarantees a nonzero secrecy data rate for the desired users as well. In addition, the obtained results unveil a tradeoff between energy efficiency and secure communication.
The purpose of this paper is to provide a novel energy-efficient perspective to the problem of contention-based synchronization in orthogonal frequency-division multiple-access communication systems. This is achieved by modeling the terminals and their corresponding receivers at the base station as economic and rational agents that engage in a noncooperative game. In the proposed game, each one trades off its available resources (transmit power and detection strategy) so as to selfishly maximize its own revenue (in terms of probability of correct detection) while saving as much energy as possible and satisfying quality-of-service requirements given in terms of probability of false alarm and timing estimation accuracy. The existence and uniqueness of the equilibrium of the game are studied. In particular, a necessary and sufficient condition on the system parameters is given for the equilibrium to exist. An iterative and distributed algorithm based on best-response dynamics (at the transmit side) and a practical parameter estimation (at the receive side) are proposed to achieve the equilibrium point. Numerical results are used to highlight the effectiveness of the proposed solution and to make comparisons with existing alternatives in terms of power consumption, synchronization time, and estimation accuracy.
Ranging is a technology for the uplink synchronization. The objective is to adjust the timing and power of mobile stations (MSs). Due to the channel effect and multiple access interference (MAI), the ranging user detection is challenged. Higher estimation accuracy usually is accompanied with higher complexity or higher resources. In view of this, we propose a feasible and practical method to achieve high performance by the differential ranging detection. At the same time, we combine the multiuser detection to overcome the MAI and the multipath effect. The most important is that the complexity of the proposed method is less than the conventional method when less ranging users transmit signals on the ranging slot.
In this paper, we propose new ranging signal designs for time-division duplexing multiple input multiple output (MIMO) orthogonal frequency division multiple access (OFDMA) systems. Exploiting the channel knowledge from the downlink channel together with initial power control, we develop three ranging transmission schemes which provide multiuser and multi-antenna diversity gains and significant power saving for the subscriber stations. The advantages of the proposed approach over existing methods in terms of ranging performance, energy saving, and complexity saving are illustrated by analytical and simulation results.
This paper addresses initial ranging (uplink synchronization and power control) for TDD OFDMA systems. Exploiting the channel knowledge from the downlink channel together with initial power control, we develop a novel initial ranging method which provides multiuser diversity gain and significant power saving for the subscriber stations. We present new ranging signal designs which enable multiuser diversity gain and facilitate new efficient low-complexity algorithms for multiuser ranging signal detection, timing estimation and power estimation. The advantages of the proposed approach over existing methods in terms of the ranging signal detection performance, the number of ranging frames required to finish the ranging process (latency at the network entry), the timing and power estimation performance, the ranging transmission power saving at the subscriber stations, and the complexity saving at the base station are illustrated by analytical and simulation results.
In this letter, we propose a successive multiuser detector (SMUD) for contention based OFDMA ranging channel compliant to the IEEE 802.16 (WiMAX) standard. A ranging channel consists of a set of subcarriers in specific time slots shared by multiple users, so the multiple access interference (MAI) limits the performance of ranging detectors. Different from existing methods that treat the MAI as noise, the proposed SMUD successively detects the channel paths of active ranging signals and cancels their interference for further detection. This approach significantly suppresses the MAI and improves both user detection and parameter estimation performance.
