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code assignment and the multicode sense scheme in an inter-vehicle CDMA communication network

IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES 1998年第11期E81A卷 2327-2333页

作者： Nagaosa, T Hasegawa, T Saitama Univ Fac Engn Dept Elect & Elect Syst Engn Urawa Saitama 3388570 Japan

This paper describes code assignment and the multicode sense scheme for an inter-vehicle CDMA communication network. When considering an inter-vehicle broadcasting CDMA communication network, spreading code assignment and notification problems arise. In such a CDMA network, the use of common codes is a solution. Then an objective function of common code assignment in an IVCN is formulated as a combinatorial optimization problem. In addition, a multicode sense (MCS)/CDMA system is proposed as a simple code assignment scheme. Computer simulations show that the MCS/CDMA system can autonomously perform spatial rearrangement of the common codes using only local information that each vehicle can obtain by sensing the code channels.

关键词： intelligent transport systems inter-vehicle communication CDMA code assignment multicode sense

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code assignment FOR HIDDEN TERMINAL INTERFERENCE AVOIDANCE IN MULTIHOP PACKET RADIO NETWORKS

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IEEE-ACM TRANSACTIONS ON NETWORKING 1995年第4期3卷 441-449页

作者： BERTOSSI, AA BONUCCELLI, MA UNIV PISA DIPARTIMENTO INFORMAT I-56100 PISA ITALY

Hidden terminal interference is caused by the (quasi-) simultaneous transmission of two stations that cannot hear each other, but are both received by the same destination station, This interference lowers the system throughput and increases the average packet delay, Some random access protocols that reduce this interference have been proposed, e.g., BTMA protocol, However, the hidden terminal interference can be totally avoided only by means of code division multiple access (CDMA) schemes, In this paper, we investigate the problem of assigning orthogonal codes to stations so as to eliminate the hidden terminal interference, Since the codes share the fixed channel capacity allocated to the network in the design stage, their number must not exceed a given bound. In this paper, we seek for assignments that minimize the number of codes used, We show that this problem is NP-complete, and thus computationally intractable, even for very restricted but very realistic network topologies. Then, we present optimal algorithms for further restricted topologies, as well as fast suboptimal centralized and distributed heuristic algorithms, The results of extensive simulation set up to derive the average performance of the proposed heuristics on realistic network topologies are presented.

关键词： code Division Multiple Access Channel Capacity Network Topology Packet Radio Networks Radiofrequency Interference Delays Minimisation Computational Complexity Interference Suppression Hidden Terminal Interference Avoidance Multihop Packet Radio Networks code assignment System Throughput Average Packet Delay code Division Multiple Access Orthogonal codes Channel Capacity NP Complete Problem Network Topologies Optimal Algorithms Distributed Heuristic Algorithms Suboptimal Centralized Algorithms Network Topology Access Protocols Multiaccess Communication Throughput Delay Interference Elimination Channel Capacity Computer Networks Heuristic Algorithms Computational Modeling

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Adaptive code assignment Algorithm for a Multi-User/Multi-Rate CDMA System

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IEICE TRANSACTIONS ON COMMUNICATIONS 2009年第5期E92B卷 1600-1607页

作者： Yu, Qiyue Adachi, Fumiyuki Meng, Weixiao Harbin Inst Technol Dept Commun Engn Harbin 150080 Heilongjiang Peoples R China Tohoku Univ Grad Sch Engn Dept Elect & Commun Engn Sendai Miyagi 9808579 Japan

code division multiple access (CDMA) technique is used widely since it can flexibly support multi-rate multi-media services by changing the number of orthogonal spreading codes. In this paper, we present a new adaptive code assignment algorithm, which consists of three steps: reserved-space, improved-crowded-first-space, and multi-code combination to fully use the code space. Compared with the existing algorithms, the proposed algorithm can avoid the code blocking problem and lower its total blocking probability while keeping its computational complexity relatively low, Simulation results show that increasing the free space reduces the average total blocking probability while increasing the blocking probability of high rate users.

关键词： code assignment code tree cost function DCA CDMA

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Smart antenna based OVSF code assignment for WCDMA networks

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WIRELESS PERSONAL COMMUNICATIONS 2007年第4期43卷 1761-1766页

作者： Kavak, Adnan Karakoc, Mustafa Kocaeli Univ Wireless Commun & Informat Syst Res Ctr Dept Comp Engn TR-41040 Izmir Turkey Turkcell Telecommun Serv Radio Network Div TR-34880 Istanbul Turkey

This paper presents a new method for dynamic allocation of orthogonal variable spreading factor (OVSF) codes in WCDMA networks where each base station is equipped with an adaptive antenna array (AAA). Previous works about OVSF code assignment problem deal with the code limitedcase. Here, we investigate the feasibility to turn the problem into the SIR limited case. With our scheme, the new call request is allocated an OVSF code that may be currently used by an active user whose downlink beam has the smallest spatial correlation with the channel vector of the requesting user, as long as desired SIR level is achieved. The performance of the new scheme is justified through computer simulations under different traffic load conditions.

关键词： adaptive antenna arrays OVSF resource management spatial diversity WCDMA code assignment smart antennas 3G SIR estimation spectral efficiency

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An integrated CDMA code assignment model for voice and data traffic in wireless communications

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IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS 2005年第2期4卷 528-537页

作者： Sheu, TL Hou, JH Natl Sun Yat Sen Univ Dept Elect Engn Kaohsiung Taiwan

Wireless personal communication requires a provision of integrated services of multimedia traffic, such as voice and data, over the radio link. The multiple access protocols of code-division multiple-access (CDMA) techniques have been widely investigated in the recent literature. This paper presents an innovative multiple access protocol for CDMA-based wireless communication systems by fully utilizing the characteristics of voice and data traffic. In other words, a voice terminal can reserve a spreading code to transmit packets in multiple talk spurts, while a data terminal can transmit packets by either using the unassigned codes or borrowing the codes from the voice terminals during their silent periods. We build mathematical models for voice and data subsystems, respectively. Two performance parameters, the average dropping probability for voice packets and the average transmission delay for data packets, are derived based on the equilibrium point analysis. The effects of the two performance parameters on the system performance are discussed by varying the code reservation intervals of the voice terminals.

关键词： code assignment code-division multiple-access (CDMA) integrated video and data traffic Markov models wireless communications

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Markov-based OVSF code assignment scheme and call admission control for wideband-CDMA communication systems

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WIRELESS PERSONAL COMMUNICATIONS 2005年第4期34卷 373-394页

作者： Chang, BJ Chen, MX Hwang, RH Chuang, CH Chaoyang Univ Technol Dept Comp Sci & Informat Engn Taichung Taiwan Natl Chung Cheng Univ Dept Comp Sci & Informat Engn Chiayi 62117 Taiwan

For the reason of the orthogonal characteristic of the Orthogonal Variable Spreading Factor (OVSF) code tree in Wideband CDMA (WCDMA) systems, code blocking increases as traffic load (i.e. Erlang load) or the required rate increases. This causes inefficient utilization of channelization codes. Hence, how to efficiently manage the resource of channelization codes of the OVSF code tree in WCDMA systems is an important issue and has been studied extensively. There are two aspects to achieve efficiency including code assignment and code reassignment. In the aspect of code assignment, an efficient code assignment scheme reduces code blocking probability significantly. In the aspect of code reassignment, code reassignment results in several drawbacks, such as large overhead of computation, high complexity of codes moving, and long call setup time for a new request call, etc. Therefore, in this paper we focus on the first aspect of how to efficiently assign the channelization codes. Additionally, most researches did not consider the analysis of tree state with dynamic traffic load and their analysis lack of systematic call admission control (CAC) mechanism. Therefore, in this paper, we first propose the Markov decision process (MDP) based analysis to assign channelization codes efficiently. Next, we extend the MDP-based approach as the call admission control mechanism to maximize the system revenue while reducing blocking probability. Furthermore, a bit string masking algorithm is proposed to reduce the time complexity of tree managing and searching for available channelization codes. Numerical results indicate that the proposed MDP approach yields the best fractional reward loss, code blocking reward loss, and code blocking ratio as compared to that of other schemes, including the random, left most, and crowded first schemes.

关键词： MDP OVSF code assignment CAC WCDMA 3G networks

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An interference avoidance code assignment strategy for downlink multi-rate MC-DS-CDMA with TF-domain spreading

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IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS 2007年第7期6卷 2508-2518页

作者： Wang, Li-Chun Chang, Chih-Wen Huang, Howard Natl Chiao Tung Univ Dept Commun Engn Hsinchu 300 Taiwan Natl Cheng Kung Univ Inst Comp & Commun Engn Tainan 701 Taiwan Alcatel Lucent Technol Holmdel NJ 07733 USA

Frequency selective fading may affect the orthogonality of the spreading codes in the multi-carrier direct sequence code division multiple access (MC-DS-CDMA) systems. In this paper, we define a new performance metric called the multiple access interference (MAI) coefficient for the MC-DS-CDMA system to quantitatively predict the impact of inter-code interference with the time- and frequency-domain spreading in a frequency selective fading channel. With the help of MAI coefficient, a novel interference avoidance code assignment strategy is proposed. By jointly considering the incurred MAI effect and the blocking probability in the code tree structure, the proposed interference avoidance code assignment method can effectively reduce the MAI for the multi-rate MC-DS-CDMA system, while maintaining very good call blocking rate performance.

关键词： code assignment interference avoidance MAI coefficient MC-DS-CDMA

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Combined equalisation and code assignment for expanded time-frequency OFDM system

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ELECTRONICS LETTERS 2010年第7期46卷 534-535页

作者： Wu, B. Shang, Y. Xiang, H. Peking Univ Sch Elect Engn & Comp Sci Beijing 100871 Peoples R China

Proposed is an effective approach to suppress noise interference in wireless communications, the expanded time-frequency (ETF-) OFDM system with joint time-frequency spreading. However, in this system, the orthogonality of the spreading code can be destroyed by multipath fading. Developed is a scheme that employs a zero-forcing equaliser at the receiver and assigns spreading codes at the transmitter for this system. Simulation results show that the ETF-OFDM system with the proposed scheme can take advantage of multipath fading to boost performance.

关键词： OFDM modulation code assignment code division multiple access codes equalisation assignment expanded time-frequency OFDM system fading channels interference suppression joint time-frequency spreading multipath fading noise interference suppression orthogonal frequency division multiplexing spread spectrum communication zero-forcing equaliser

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Efficient OVSF code assignment and reassignment strategies in UMTS

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IEEE TRANSACTIONS ON MOBILE COMPUTING 2006年第7期5卷 769-783页

作者： Chen, Min-Xiou Hwang, Ren-Hung Natl Chung Cheng Univ Dept Comp Sci & Informat Engn Chiayi Taiwan

This paper presents an integrated solution for code management, assignment, and reassignment problems in UMTS. We propose a new architecture for code management and, based upon this new architecture, a code assignment strategy, referred to as "crowded-group first strategy." Our system architecture and code assignment strategy represent significant improvements both in the time complexity and the maintenance complexity. Moreover, the code blocking probability of the crowded-group first strategy is competitive to that of the other strategies. In this paper, we also propose a new code reassignment strategy, called the "crowded-branch first strategy." The main objective of this reassignment strategy is to reduce reassigned call probability with low computation overhead and extend this strategy for the general case. In order to systematically analyze the performances of the code assignment strategy, we implement a simulator to analyze the code selection behavior and code blocking probability of each strategy. Moreover, we propose some new performance metrics, named "weighted code blocking," " reassigned call probability," and " ratio of actual code reassignments," in order to precisely measure the performance obtained by different strategies. From the simulation results, we show that our proposed strategies efficiently utilize the OVSF codes with low computation overhead.

关键词： code assignment dynamic code assignment OVSF code wideband CDMA resource management

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An algorithmic view on OVSF code assignment

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ALGORITHMICA 2007年第3期47卷 269-298页

作者： Erlebach, Thomas Jacob, Riko Mihalak, Matus Nunkesser, Marc Szabo, Abor Widmayer, Peter Univ Leicester Dept Comp Sci Leicester LE1 7RH Leics England ETH Dept Comp Sci CH-8092 Zurich Switzerland

Orthogonal Variable Spreading Factor (OVSF) codes are used in UMTS to share the radio spectrum among several connections of possibly different bandwidth requirements. The combinatorial core of the OVSF code assignment problem is to assign some nodes of a complete binary tree of height h ( the code tree) to n simultaneous connections, such that no two assigned nodes ( codes) are on the same root-to-leaf path. A connection that uses a 2(-d) fraction of the total bandwidth requires some code at depth d in the tree, but this code assignment is allowed to change over time. Requests for connections that would exceed the total available bandwidth are rejected. We consider the one-step code assignment problem: Given an assignment, move the minimum number of codes to serve a new request. Minn and Siu propose the so-called DCA algorithm to solve the problem optimally. In contrast, we show that DCA does not always return an optimal solution, and that the problem is NP-hard. We give an exact n(O(h))-time algorithm, and a polynomial-time greedy algorithm that achieves approximation ratio Theta(h). A more practically relevant version is the online code assignment problem, where future requests are not known in advance. Our objective is to minimize the overall number of code reassignments. We present a Theta(h)-competitive online algorithm, and show that no deterministic online algorithm can achieve a competitive ratio better than 1.5. We show that the greedy strategy ( minimizing the number of reassignments in every step) is not better than Omega(h) competitive. We give a 2-resource augmented online algorithm that achieves an amortized constant number of (re-) assignments. Finally, we show that the problem is fixed-parameter tractable.

关键词： OVSF codes code assignment approximation algorithms online algorithms

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