OFDM系统中自适应调制与编码技术研究
|
摘要
正交频分复用技术(Orthogonal Frequency Division Multiplexing)是一种多载波调制技术,具有频谱利用率高、调制方式灵活、抗多径干扰能力强等特点,已成为第四代无线通信系统中物理层的核心调制技术。自适应调制与编码技术(Adaptive Modulation and Coding)能够根据信道状态信息自适应地选择调制与编码方案,因而能够最大限度地提高系统吞吐量,保证目标误帧率。随着用户需求的增加,下一代通信网络中将承载大量的IP分组业务和高速数据业务,为保证传输质量,提高传输速率,将自适应调制与编码技术应用于OFDM系统是一个必然的趋势。
本文研究了OFDM系统中的自适应调制与编码技术,主要研究内容和工作成果如下:
1.系统阐述了OFDM技术和OFDM系统自适应调制的基本原理,给出了几种典型的OFDM自适应调制算法的实现步骤,并比较了其优缺点。
2.采用Matlab仿真软件建立了OFDM基带模型,对不同条件下OFDM系统的误码性能进行了仿真,并给出了比较分析的结果,为实际的系统应用提供了理论参考。
3.提出了一种复杂度较低的联合自适应帧长的自适应调制与编码方案。该方案建立在理想信道估计的基础上,采用平均功率分配,实现比较简单。采用平均信道误比特率作为联合自适应编码和自适应调制过程的参数。在不同的噪声环境中,根据给定的目标误帧率为不同的编码方式设定不同的平均信道误比特率,结合各个子载波的瞬时信道状态信息进行比特分配,通过计算选择频谱效率最大的编码方式,从而完成自适应调制与编码。仿真结果表明,该方案能保证系统误帧率性能,与宽带无线网络中广泛采用的固定阈值自适应调制与编码方案相比,该方案能够有效提高数据传输速率。
OFDM is a multi-carrier transmission technique for wireless communication system. Due to its high data rate transmission capacity with high spectral efficiency, flexible modulation modes and its robustness to multi-path delay, OFDM has been the core physical technique in the fourth generation communication systems. With variable code, variable power and variable rate, adaptive modulation and coding can provide high throughput under the frame error rate constraint. In the next generation communication systems, there are plenty of IP packet and high-rate data services. To guarantee the transmission quality and enhance the transmission rate, it is an inevitable tendency to apply adaptive modulation and coding to OFDM systems.
Policies of adaptive modulation and coding in OFDM systems are studied in this paper. The main researches and contributions are as follows:
1. In this paper, the principles of OFDM technique and adaptation of modulation in OFDM system are first introduced. Typical algorithms for adaptive modulation are summarized and compared.
2. With Matlab software, a simulation model of a baseband OFDM system is established. The BER performance under different conditions are simulated and compared. The simulation results prove the validity of OFDM technique and can provide a valuable theoretic reference to practical application.
3. An adaptive modulation and coding scheme combining adaptive frame length is proposed. With uniform power allocation, the complexity the proposed scheme is low. The average channel bit error rate is the key parameter to combine adaptive coding and adaptive modulation. In different noise environments, different parameters are set for different coding schemes given the target frame error rate. Using these parameters, we complete rate allocation according to the instantaneous channel state information. And the coding scheme with the highest spectral efficiency will be selected. Simulation results show that the proposed scheme has a satisfying FER. Compared to the widely used policy with fixed threshold, the proposed scheme improves the transmission rate effectively.
本文研究了OFDM系统中的自适应调制与编码技术,主要研究内容和工作成果如下:
1.系统阐述了OFDM技术和OFDM系统自适应调制的基本原理,给出了几种典型的OFDM自适应调制算法的实现步骤,并比较了其优缺点。
2.采用Matlab仿真软件建立了OFDM基带模型,对不同条件下OFDM系统的误码性能进行了仿真,并给出了比较分析的结果,为实际的系统应用提供了理论参考。
3.提出了一种复杂度较低的联合自适应帧长的自适应调制与编码方案。该方案建立在理想信道估计的基础上,采用平均功率分配,实现比较简单。采用平均信道误比特率作为联合自适应编码和自适应调制过程的参数。在不同的噪声环境中,根据给定的目标误帧率为不同的编码方式设定不同的平均信道误比特率,结合各个子载波的瞬时信道状态信息进行比特分配,通过计算选择频谱效率最大的编码方式,从而完成自适应调制与编码。仿真结果表明,该方案能保证系统误帧率性能,与宽带无线网络中广泛采用的固定阈值自适应调制与编码方案相比,该方案能够有效提高数据传输速率。
OFDM is a multi-carrier transmission technique for wireless communication system. Due to its high data rate transmission capacity with high spectral efficiency, flexible modulation modes and its robustness to multi-path delay, OFDM has been the core physical technique in the fourth generation communication systems. With variable code, variable power and variable rate, adaptive modulation and coding can provide high throughput under the frame error rate constraint. In the next generation communication systems, there are plenty of IP packet and high-rate data services. To guarantee the transmission quality and enhance the transmission rate, it is an inevitable tendency to apply adaptive modulation and coding to OFDM systems.
Policies of adaptive modulation and coding in OFDM systems are studied in this paper. The main researches and contributions are as follows:
1. In this paper, the principles of OFDM technique and adaptation of modulation in OFDM system are first introduced. Typical algorithms for adaptive modulation are summarized and compared.
2. With Matlab software, a simulation model of a baseband OFDM system is established. The BER performance under different conditions are simulated and compared. The simulation results prove the validity of OFDM technique and can provide a valuable theoretic reference to practical application.
3. An adaptive modulation and coding scheme combining adaptive frame length is proposed. With uniform power allocation, the complexity the proposed scheme is low. The average channel bit error rate is the key parameter to combine adaptive coding and adaptive modulation. In different noise environments, different parameters are set for different coding schemes given the target frame error rate. Using these parameters, we complete rate allocation according to the instantaneous channel state information. And the coding scheme with the highest spectral efficiency will be selected. Simulation results show that the proposed scheme has a satisfying FER. Compared to the widely used policy with fixed threshold, the proposed scheme improves the transmission rate effectively.
引文
[1] Theodore, S. Rappaport 著. 蔡涛, 李旭, 杜振民译. 无线通信原理与应用. 电子工业出版社, 1999, 123-125
[2] 佟学俭, 罗涛. OFDM 移动通信技术原理与应用. 人民邮电出版社, 2003, 30-35
[3] 宋平, 胡爱群. 链路自适应技术在 IEEE802.16 系统中的应用. 解放军理工大学学报(自然科学版), 2006, 7(6): 510-513
[4] J. Yang, N. Tin, A.K. Khandani. Adaptive modulation and coding in 3G wireless systems. In: Proceedings of IEEE Vehicular Technology Conference, 2002, 1: 544-548
[5] S.B. Weinstein, P.M. Ebert. Data transmission by frequency-division multiplexing using the discrete Fourier transforms. IEEE Transactions on Communications, 1971, 19(5): 628-634
[6] LAN MAN Standards Committee. IEEE P802.16REVd: Air interface for fixed broadband wireless access systems. IEEE Computer Society, 2004: 401-451
[7] Richard van Nee, Armout de wild. Reducing the peak-to-average power ratio of OFDM. In: Proceedings of IEEE Vehicular Technology Conference, 1998, Ottawa, 3: 2072-2076
[8] Mizhou Tan, J.Cheng, Y. Bar-Ness. OFDM peak power reduction by a novel coding scheme with threshold control. In: Proceedings of IEEE Vehicular Technology Conference, 2001, Atlantic, 2: 669-672
[9] Pollet T, M. van Bladel, M. Moeneclaey. BER sensitivity of OFDM systems to carrier frequency offset and Wiener phase noise. IEEE Transactions on Communications, 1995, 43(234): 191-193
[10] Pollet T, M. Moeneclaey. Synchronizability of OFDM signals. In: Proceedings of IEEE Global Telecommunications Conference, 1995, 3: 2054-2058
[11] J.-J. van de Beek, O. Edfors, M. Sandell, S.K. Wilson, P.O. Borjesson. On channel estimation in OFDM systems. In: Proceedings of IEEE Vehicular Technology Conference, 1995, 2: 815-819
[12] C.R.N. Athaudage, A.D.S. Jayalath. Enhanced MMSE channel estimation using timing error statitics for wireless OFDM systems. IEEE Transactions onBroadcasting, 2004, 50(4): 369-376
[13] 曹志刚, 钱亚生. 现代通信原理. 清华大学出版社, 2001, 322-325
[14] 程宇新, 项海格. 自适应调制混合 ARQ 系统中低时延冗余递增策略的研究. 电子与信息学报, 2006, 28(9): 1649-1653
[15] J. Hayes. Adaptive feedback communications. IEEE Transactions on Communications, 1968, 16(1): 29-34
[16] A.J. Goldsmith, S.G. Chua. Variable-rate variable–power MQAM for fading channels. IEEE Transactions on Communications, 1997, 45(10): 1218-1230
[17] J. Torrance, L. Hanzo. Optimisation of switching levels for adaptive modulation in a slow Rayleigh fading channel. Electronics Letters, 1996, 32(13): 1167-1169
[18] B.J. Choi, L. Hanzo. Optimum mode-switching-assisted constant-power single- and multicarrier adaptive modulation. IEEE Transactions on Vehicular Technology, 2003, 52(3): 536-560
[19] T. Keller, L. Hanzo. Adaptive multicarrier modulation: A convenient framework for time-frequency processing in wireless communications. In: Proceedings of the IEEE, 2000, 88(5): 611-640
[20] 余官定, 张朝阳, 仇佩亮. OFDM 系统功率和比特分配算法研究. 电子与信息学报, 2005, 27(9): 1479-1482
[21] D. Kivanc, H. Liu. Subcarrier allocation and power control for OFDMA. In: Conference Record of the Thirty-Fourth Asilomar Conference, 2000, 1: 147-151
[22] A. Czylwik. Adaptive OFDM for wideband radio channels. In: Proceedings of IEEE Global Telecommunications Conference, 1996, London, 1: 713-718
[23] C.Y. Wong, R.S. Cheng, K.B. Letaief, R.D. Murch. Multiuser OFDM with adaptive subcarrier, bit, and power allocation. IEEE Journal on Selected Areas in Communications, 1999, 17(10): 1747-1758
[24] 郭凯, 孙群龙, 卫国, 朱近康. OFDM 系统中多业务间子载波借调自适应资源分配算法. 电子与信息学报, 2006, 28(8): 1345-1349
[25] 龚汉东, 叶梧, 冯穗力, 柯峰. 多用户 OFDM 系统的子载波分配算法. 华南理工大学学报(自然科学版), 2006, 34(6): 12-16
[26] 范晨, 陈美娅, 苏丽君, 杨大成. 自适应调制编码系统门限调整算法研究. 北京邮电大学学报, 2006, 29(4): 49-53
[27] T. Onodera, T. Nogami, O. Nakamura, N. Okamoto. AMC design for wideband maintaining target quality over time-varing channels. In: Proceeding of Personal, Indoor and Mobile Radio Communications, 2007: 1-5
[28] K.B .Song, A. Ekbal, S.T. Chung, J.M. Cioffi. Adaptive modulation and codingfor bit-interleaved coded OFDM(BIC-OFDM). IEEE Transactions on Wireless Communications, 2006, 5(7): 1685-1694
[29] 余官定, 张朝阳, 仇佩亮. 信道粒度可变的分块自适应 OFDM 传输系统. 电路与系统学报, 2004, 9(5): 53-57
[30] Xiaoming She, Shidong Zhou, Xibin Xu, Yan Yao. Power and bit allocation for adaptive turbo coded modulation in OFDM systems. In: Proceedings of IEEE Global Telecommunications Conference, 2003, 2: 903-907
[31] S.G. Chua, A.J. Goldsmith. Adaptive coded modulation for fading channels. IEEE Transaction on communications, 1998, 46(5): 595-602
[32] S.K. Lai, R.S. Cheng, K.B. Letaief, R.D. Murch. Adaptive trellis coded MQAM and power optimization for OFDM transmission. In: Proceedings of IEEE Vehicular Technology Conference, 1999, Houston, 1: 290-295
[33] 杨家玮, 盛敏, 刘勤. 移动通信基础. 电子工业出版社, 2005, 37-41
[34] 李颖, 王新梅. 块衰落信道下多层空时分组码设计与容量分析. 通信学报, 2003, 24(11A): 8-15
[35] 薛得志, 赵新胜. 一种联合 AMC 和自适应帧长技术的 ARQ 方案. 军事通信技术, 2005, 26(增刊): 28-31
[36] Simon Haykin 著. 宋铁城, 徐平平, 徐智勇译. 通信系统. 电子工业出版社, 2003: 376-377
[37] P.S. Chow, J.M. Cioffi, J.A.C Bingham. A practical discrete multitone transceiver loading algorithm for data transmission over spectrally shaped channels. IEEE Transactions on Communications, 1995, 43(234): 773-775
[38] R.F.H Fischer, J.B. Huber. A new loading algorithm for discrete multitone transmission. In: Proceedings of IEEE Global Telecommunications Conference, London, 1996, 1: 724-728
[39] T. Keller, L. Hanzo. Adaptive modulation and techniques for duplex OFDM transmission. IEEE Transactions on Vehicular Technology, 2000, 49(5): 1893-1906
[40] J. Hagenauer. Rate-compatible punctured convolutional codes (RCPC) and their applications. IEEE Transactions on Communications,1988, 36(4): 389-400
[41] Y. Yasuda, K. Kashiki, Y. Hirata. High-rate convolutional codes for soft decision viterbi decoding. IEEE Transactions on Communications, 1984, 32(3): 316-319
[42] 袁东风, 李作为, 张锋. Punctured(2,1,N)系列卷积码的编码及其 Viterbi 译码的软件实现. 山东大学学报(自然科学版), 2002, 37(1): 48-53
[43] E. Malkam?ki, H. Leib. Evaluating the performance of convolutional codes over blocking fading channels. IEEE Transactions on Information Theory, 1999, 45(5): 1643-1646
[44] A.J. Viterbi. Convolutional codes and their performance in communication systems. IEEE Transactions on Communications Technology, 1971, 19(5): 751-772
[45] J. Torrance, L. Hanzo. Upper bound performance of adaptive modulation in a slow Rayleighfading channel. Electronics Letters, 1996, 32(8): 718-719
[46] S. T. Chung, A. J. Goldsmith. Degrees of freedom in adaptive modulation: a unified view. IEEE Transactions on Communications, 2001, 49(9): 1561–1571
[2] 佟学俭, 罗涛. OFDM 移动通信技术原理与应用. 人民邮电出版社, 2003, 30-35
[3] 宋平, 胡爱群. 链路自适应技术在 IEEE802.16 系统中的应用. 解放军理工大学学报(自然科学版), 2006, 7(6): 510-513
[4] J. Yang, N. Tin, A.K. Khandani. Adaptive modulation and coding in 3G wireless systems. In: Proceedings of IEEE Vehicular Technology Conference, 2002, 1: 544-548
[5] S.B. Weinstein, P.M. Ebert. Data transmission by frequency-division multiplexing using the discrete Fourier transforms. IEEE Transactions on Communications, 1971, 19(5): 628-634
[6] LAN MAN Standards Committee. IEEE P802.16REVd: Air interface for fixed broadband wireless access systems. IEEE Computer Society, 2004: 401-451
[7] Richard van Nee, Armout de wild. Reducing the peak-to-average power ratio of OFDM. In: Proceedings of IEEE Vehicular Technology Conference, 1998, Ottawa, 3: 2072-2076
[8] Mizhou Tan, J.Cheng, Y. Bar-Ness. OFDM peak power reduction by a novel coding scheme with threshold control. In: Proceedings of IEEE Vehicular Technology Conference, 2001, Atlantic, 2: 669-672
[9] Pollet T, M. van Bladel, M. Moeneclaey. BER sensitivity of OFDM systems to carrier frequency offset and Wiener phase noise. IEEE Transactions on Communications, 1995, 43(234): 191-193
[10] Pollet T, M. Moeneclaey. Synchronizability of OFDM signals. In: Proceedings of IEEE Global Telecommunications Conference, 1995, 3: 2054-2058
[11] J.-J. van de Beek, O. Edfors, M. Sandell, S.K. Wilson, P.O. Borjesson. On channel estimation in OFDM systems. In: Proceedings of IEEE Vehicular Technology Conference, 1995, 2: 815-819
[12] C.R.N. Athaudage, A.D.S. Jayalath. Enhanced MMSE channel estimation using timing error statitics for wireless OFDM systems. IEEE Transactions onBroadcasting, 2004, 50(4): 369-376
[13] 曹志刚, 钱亚生. 现代通信原理. 清华大学出版社, 2001, 322-325
[14] 程宇新, 项海格. 自适应调制混合 ARQ 系统中低时延冗余递增策略的研究. 电子与信息学报, 2006, 28(9): 1649-1653
[15] J. Hayes. Adaptive feedback communications. IEEE Transactions on Communications, 1968, 16(1): 29-34
[16] A.J. Goldsmith, S.G. Chua. Variable-rate variable–power MQAM for fading channels. IEEE Transactions on Communications, 1997, 45(10): 1218-1230
[17] J. Torrance, L. Hanzo. Optimisation of switching levels for adaptive modulation in a slow Rayleigh fading channel. Electronics Letters, 1996, 32(13): 1167-1169
[18] B.J. Choi, L. Hanzo. Optimum mode-switching-assisted constant-power single- and multicarrier adaptive modulation. IEEE Transactions on Vehicular Technology, 2003, 52(3): 536-560
[19] T. Keller, L. Hanzo. Adaptive multicarrier modulation: A convenient framework for time-frequency processing in wireless communications. In: Proceedings of the IEEE, 2000, 88(5): 611-640
[20] 余官定, 张朝阳, 仇佩亮. OFDM 系统功率和比特分配算法研究. 电子与信息学报, 2005, 27(9): 1479-1482
[21] D. Kivanc, H. Liu. Subcarrier allocation and power control for OFDMA. In: Conference Record of the Thirty-Fourth Asilomar Conference, 2000, 1: 147-151
[22] A. Czylwik. Adaptive OFDM for wideband radio channels. In: Proceedings of IEEE Global Telecommunications Conference, 1996, London, 1: 713-718
[23] C.Y. Wong, R.S. Cheng, K.B. Letaief, R.D. Murch. Multiuser OFDM with adaptive subcarrier, bit, and power allocation. IEEE Journal on Selected Areas in Communications, 1999, 17(10): 1747-1758
[24] 郭凯, 孙群龙, 卫国, 朱近康. OFDM 系统中多业务间子载波借调自适应资源分配算法. 电子与信息学报, 2006, 28(8): 1345-1349
[25] 龚汉东, 叶梧, 冯穗力, 柯峰. 多用户 OFDM 系统的子载波分配算法. 华南理工大学学报(自然科学版), 2006, 34(6): 12-16
[26] 范晨, 陈美娅, 苏丽君, 杨大成. 自适应调制编码系统门限调整算法研究. 北京邮电大学学报, 2006, 29(4): 49-53
[27] T. Onodera, T. Nogami, O. Nakamura, N. Okamoto. AMC design for wideband maintaining target quality over time-varing channels. In: Proceeding of Personal, Indoor and Mobile Radio Communications, 2007: 1-5
[28] K.B .Song, A. Ekbal, S.T. Chung, J.M. Cioffi. Adaptive modulation and codingfor bit-interleaved coded OFDM(BIC-OFDM). IEEE Transactions on Wireless Communications, 2006, 5(7): 1685-1694
[29] 余官定, 张朝阳, 仇佩亮. 信道粒度可变的分块自适应 OFDM 传输系统. 电路与系统学报, 2004, 9(5): 53-57
[30] Xiaoming She, Shidong Zhou, Xibin Xu, Yan Yao. Power and bit allocation for adaptive turbo coded modulation in OFDM systems. In: Proceedings of IEEE Global Telecommunications Conference, 2003, 2: 903-907
[31] S.G. Chua, A.J. Goldsmith. Adaptive coded modulation for fading channels. IEEE Transaction on communications, 1998, 46(5): 595-602
[32] S.K. Lai, R.S. Cheng, K.B. Letaief, R.D. Murch. Adaptive trellis coded MQAM and power optimization for OFDM transmission. In: Proceedings of IEEE Vehicular Technology Conference, 1999, Houston, 1: 290-295
[33] 杨家玮, 盛敏, 刘勤. 移动通信基础. 电子工业出版社, 2005, 37-41
[34] 李颖, 王新梅. 块衰落信道下多层空时分组码设计与容量分析. 通信学报, 2003, 24(11A): 8-15
[35] 薛得志, 赵新胜. 一种联合 AMC 和自适应帧长技术的 ARQ 方案. 军事通信技术, 2005, 26(增刊): 28-31
[36] Simon Haykin 著. 宋铁城, 徐平平, 徐智勇译. 通信系统. 电子工业出版社, 2003: 376-377
[37] P.S. Chow, J.M. Cioffi, J.A.C Bingham. A practical discrete multitone transceiver loading algorithm for data transmission over spectrally shaped channels. IEEE Transactions on Communications, 1995, 43(234): 773-775
[38] R.F.H Fischer, J.B. Huber. A new loading algorithm for discrete multitone transmission. In: Proceedings of IEEE Global Telecommunications Conference, London, 1996, 1: 724-728
[39] T. Keller, L. Hanzo. Adaptive modulation and techniques for duplex OFDM transmission. IEEE Transactions on Vehicular Technology, 2000, 49(5): 1893-1906
[40] J. Hagenauer. Rate-compatible punctured convolutional codes (RCPC) and their applications. IEEE Transactions on Communications,1988, 36(4): 389-400
[41] Y. Yasuda, K. Kashiki, Y. Hirata. High-rate convolutional codes for soft decision viterbi decoding. IEEE Transactions on Communications, 1984, 32(3): 316-319
[42] 袁东风, 李作为, 张锋. Punctured(2,1,N)系列卷积码的编码及其 Viterbi 译码的软件实现. 山东大学学报(自然科学版), 2002, 37(1): 48-53
[43] E. Malkam?ki, H. Leib. Evaluating the performance of convolutional codes over blocking fading channels. IEEE Transactions on Information Theory, 1999, 45(5): 1643-1646
[44] A.J. Viterbi. Convolutional codes and their performance in communication systems. IEEE Transactions on Communications Technology, 1971, 19(5): 751-772
[45] J. Torrance, L. Hanzo. Upper bound performance of adaptive modulation in a slow Rayleighfading channel. Electronics Letters, 1996, 32(8): 718-719
[46] S. T. Chung, A. J. Goldsmith. Degrees of freedom in adaptive modulation: a unified view. IEEE Transactions on Communications, 2001, 49(9): 1561–1571