Cross-layer scheduling strategy for UMTS downlink enhancement

This article describes the benefits of including cross-layer information in the scheduling mechanism of a UMTS downlink channel. In particular, the information obtained from the fast power control algorithm is used to properly schedule transmissions. A prioritization function that exploits the short-term channel variations is proposed. This strategy is shown to be a feasible approach to improve system performance in terms of capacity and delay. This enhancement is obtained as a benefit of intrinsic multi-user diversity. The proposal is applicable within the current UMTS radio resource management framework.     

Mixed traffic in UMTS downlink

The traffic being transferred within 3G mobile networks will be composed by different information flows with various constraints on the required QoS (bit rate, delays, etc.). In this scenario, flexibility will be a key point for the success of 3G systems. UMTS (Universal Mobile Telecommunication System) offers both circuit switched and packet switched transfer mode, and within each transfer mode, different QoS can be achieved by properly setting physical parameters such as the spreading factor of the physical channels, the power control scheme, the rate of the FEC protecting code, etc. In this letter, we give an evaluation of the downlink performance of W-CDMA UMTS radio interface when providing access to multimedia services. In particular, we analyze through simulations a typical scenario where voice calls and Web-browsing sessions share the same frequency carrier, the former using the dedicated channels (DCH), the latter being transferred on the downlink shared channel (DSCH).     

Overflow control for UMTS high-speed downlink packet access

This paper proposes overflow control schemes to support high-speed downlink packet access (HSDPA) mechanism in the universal mobile telecommunication system (UMTS). To access the UMTS services, a user equipment (UE) communicates with all cells (base stations) in an active set. However, multiple links between the UE and the cells in the active set may reduce the transmission speed due to interference. Third-Generation Partnership Project specification TR 25.950 proposes HSDPA. In this mechanism, the UE only selects one cell (referred to as the serving cell) in the active set for high-speed downlink transmission. In HSDPA, the radio network controller sends the packet frames to the cells in the active set. For the serving cell, the packet frames are forwarded to the UE. On the other hand, every nonserving cell in the active set queues the packet frames in a buffer. If the link quality between the serving cell and the UE degrades below some threshold, the UE selects the best cell in the active set as the new serving cell. Since the nonserving cells do not send packet frames to the UE, their buffers may overflow. In this paper, we propose schemes to address the buffer overflow issue. Our schemes guarantee that when the buffer of a nonserving cell is full, the previously received packet frames in the buffer can be safely dropped, and after the UE has switched wireless link to the new serving cell, no packet frames are lost.     

Frequency synchronization for TD-LTE-A downlink receiver

A high accuracy frequency synchronization method is proposed for the 3rd generation partnership project (3GPP) long term evolution advanced (LTE-A) downlink receiver in time division duplexing (TDD) mo...     

Modeling frame synchronization for UMTS high-speed downlink packet access

Third Generation Partnership Project (3GPP) specification TR 25.950 proposed high-speed downlink packet access for the Universal Mobile Telecommunication System (UMTS). In this mechanism, an active set of cells is defined for every user equipment (UE) communication session. The cell with the best wireless link quality (called the serving cell) in the active set is selected for communication with the UE. When the wireless link quality of the old serving cell degrades below some threshold, a new serving cell in the active set is selected to continue the communication session. Our previous work proposed a high-speed downlink packet access (HSDPA) overflow control scheme with four frame synchronization algorithms to switch the serving cell, and formally proved the correctness of the scheme. We propose an analytic model to investigate the performance of these frame synchronization algorithms, and show how the user movement patterns affect the control message delivery costs of these algorithms.     

A low-complexity iterative multiuser receiver for turbo-codedDS-CDMA systems

Optimal joint multiuser detection and decoding for direct-sequence code-division multiple-access (DS-CDMA) systems with forward error correction normally requires prohibitively high computational complexity. A suboptimal solution with low complexity is therefore appealing for use in practical applications. We propose a low-complexity iterative multiuser receiver for turbo-coded DS-CDMA systems. The proposed approach consists of a modified decorrelating decision-feedback detector (MDDFD) and K single-user turbo decoders, where K is the number of users in the DS-CDMA system. The MDDFD is derived on the basis of maximizing a likelihood probability and has a feature that it can use the reliability information from the turbo decoders' output. In addition, the MDDFD can deliver interference-cancelled soft outputs to the turbo decoders where the calculation of transition metrics is modified appropriately. Both performance analysis and computer simulation results have indicated that the reliability information from the turbo decoders' output can enhance the multiuser detection capability of the MDDFD. Computer simulations have also shown that the proposed iterative multiuser receiver outperforms the conventional DDFD-based multiuser receiver in terms of the bit-error probability     

An efficient receiver scheme for downlink ZP-CDMA

A signal transmitted through a wireless channel may be severely distorted by intersymbol interference (ISI) and multiple access interference (MAI). In this paper, we propose an efficient CDMA receiver based on frequency domain equalization (FDE) with a regularized zero forcing (RZF) equalizer and parallel interference cancellation with a unit clipper decision function (CPIC) to combat both the ISI and the MAI. We call this receiver the FDE-RZF-CPIC receiver. This receiver is suitable for downlink zero padding CDMA cellular systems. The effects of the decision function, the channel estimation, the number of cancelled users, and the user loading on the performance of the proposed receiver are discussed in the paper. The bit error rate (BER) of the data received by the proposed receiver is evaluated by computer simulations. The experimental results show that the proposed receiver provides a good performance, even with a large number of interfering users. At a BER of 10^?3, the performance gain of the proposed receiver is about 2 dB over the RAKE receiver with a clipper decision function and PIC in the half-loaded case (eight users) and is much larger in the full-loaded case (16 users).     

Module count-based overflow-control scheme for UMTS high-speed downlink packet access

In the universal mobile telecommunication system, the user equipment (UE) communicates with all cells in the active set through the air interface. Multiple radio links between the UE and the cells may reduce the transmission speed due to interference. In high-speed downlink packet access (HSDPA), only one serving cell is selected in the active set for high-speed downlink transmission. When the radio link quality between the serving cell and the UE degrades below some threshold, the best cell (in terms of the radio characteristics) in the active set is selected as the new serving cell and the UE switches from the old serving cell to the new serving cell. This action is referred to as frame synchronization. The frame-synchronization information may be delivered through more than one wireless transmission, which introduces long delay for the frame-synchronization process. In this paper, we propose an overflow-control scheme with module count for HSDPA, which guarantees that the frame-synchronization information is delivered through one wireless transmission and that when the UE switches wireless link to the new serving cell, no packet frames are lost.     

Iterative receiver for OFDM-SDMA system

An iterative receiver is proposed based on the EM (Expectation-Maximization) algorithm for an OFDM-SDMA (Orthogonal Frequency Division Multiplexing-Space Division Multiple Access) system. By using a few pilots in every OFDM symbol, both channel estimation and multiuser detection can be simultaneously obtained by iteration. The computer simulation results show this receiver can track channel variations and detect multiuser symbols for different number of users under time-varying multipath channels.     

A new blind receiver for downlink DS-CDMA communications

A linear receiver is proposed for downlink DS-CDMA communications over unknown frequency-selective fading channels. The new receiver exploits the fact that all synchronized downlink signals go through the same channel and recovers the desired signal with a constrained channel equalizer followed by a despreader. Such a scheme allows the receiver to operate blindly in a time varying environment for both periodic CDMA and aperiodic CDMA systems     

WCDMA下行链路接收机设计

根据下行链路的需求设计了可以满足实时性需要的接收机。在下行链路中,只有所希望的用户信号被解调,而抑制其他用户引起的干扰。针对这一特点,下行链路接收主要采用单用户接收机,在本文中对各种单用户接收算法进行了分析、仿真及性能比较,本文的单用户接收算法采用自适应LMMS单用户接收算法。采用的接收机是在自适应LMMSE接收机基础上提出的差分自适应接收机,该接收机运算量比较小,性能比较好,并且能够跟踪同步,能够在用户终端上使用。     

Switched beams versus beam pointing for boosting the downlink capacity of UMTS FDD

In this paper the switched beam method is compared with beam pointing. Using extensive system simulations it is shown that both methods achieve a capacity gain over a 3-sectored reference system of more than 170%. As the capacity achieved with the two systems is nearly the same but the complexity of beam pointing is significantly higher, I conclude that switched beams are the appropriate method for boosting the downlink capacity of UMTS FDD.     

A low-power and low-complexity continuous-time Gm-C based Delta-Sigma modulator for WCDMA/UMTS

This article describes the implementation of a continuous-time Delta-Sigma modulator for WCDMA/UMTS in wireless communication. The Delta-Sigma modulator employs a Gm-C based integrator to form a fourth-order noise-shaping loop. The modulator samples at 160 MHz and has an over-sampling ratio of 40 in 2 MHz bandwidth. To reduce power consumption and design complexity, single-bit quantisation is employed. The modulator is implemented in 0.25 µm 1-ploy 5-metal CMOS technology and has an area of 0.13 mm². The modulator can achieve 70.7 dB of signal-to-noise-plus-distortion-ratio and 74 dB of dynamic range. Finally, the modulator consumes 3.5 mW of power with a reduced power supply of 1.8 V.     

Application and performance of downlink beamforming techniques in UMTS

The opportunities and constraints for application of beamforming techniques in UMTS are reviewed and compared by means of extensive dynamic network-level simulations. We start by reviewing the physical layer specifications for UMTS in order to clarify which channels are allowed to use beamforming. Second, radio resource management for cells with beamforming capabilities are addressed from a standardization and algorithmic point of view. The exchange of beamforming specific measurement reports between the base station (Node-B) and the radio network controller is discussed as well as beam switching mechanisms, directional power-based admission control, and more. In addition to implementation of beamforming within logical cells, options for exploiting the antenna array to synthesize independent sector beams are also investigated (i.e., higher order sectorization via beamforming). The presented results show that beamforming within logical cells is an effective enabler for higher system capacity, while the use of beamforming for creation of many logical cells is less attractive due to significantly larger soft handover overhead and somewhat reduced capacity gain.     

Imbalance-compensated direct down conversion receiver for UMTS base stations

In this work, a new method for the estimation and the compensation of in-phase quadrature-imbalances in direct down conversion receivers is presented. The considerations are based on a receiver structure that is developed for the simultaneous down conversion of up to four neighboring carriers in universal mobile telecommunications system base stations. The image suppression of the system must achieve at least 60 dB. This requirement is not fulfilled by the analogue part and hence, an error estimation and compensation in the digital domain is necessary. In laboratory measurements using a wideband code-division multiple-access signal, the image suppression of the complete set-up including the analogue parts could be improved by 34 dB.     

Iterative multiuser turbo-code receiver for DS-CDMA

A number of different iterative decoding methods are proposed for multiuser interference cancellation in a code-division multiple-access system where turbo-codes are utilized for forward error correction (FEC). The individual users are decoded separately with the operation of iterative interference cancellation being mixed with iterative decoding of the turbo-code. This results in a modest increase in the overall complexity as compared to a conventional single-user receiver utilizing turbo-code for FEC. Numerical results are presented showing that the proposed iterative decoders show an improvement in the bit error rate performance and/or a reduction in the computational complexity as compared to similar previously known methods reported by M.C. Reed et al. (see 8th IEEE Int. Symp. Personal, Indoor and Mobile Radio Commun. - PIMRC'97, vol.2, p.740-4, 1997; IEEE Trans. Commun., vol.46, p.1693-9, 1998).     

BER evaluation and rate matching attribute selection for QoS support on the UMTS downlink

In UMTS technology, Coded Composite Transport Channels (CCTrCh-s) are used to carry multiple Transport Channels (TrCh-s) in parallel on (usually) one physical layer connection. Rate Matching Attributes (RMA-s) are used to share the CCTrCh resources among the transport channels. We consider I transport channels on the downlink of a UMTS network, with RMA values RMA ₁,RMA ₂,…,RMA _I . The QoS experienced by the multiplexed connections depends on the RMA values used. We derive analytical expressions for the Bit Error Probabilities (BER-s) seen by each uncoded TrCh in the multiplex when transmitted over an AWGN and a multipath channel. Simulations indicate that the expressions are very accurate. Next, we derive analytical expressions for bounds on the per-channel bit error probabilities seen when convolutional coding is employed by each channel and the multiplex is transmitted over an AWGN and a multipath channel, respectively. The derivation of these analytical expressions is the main contribution of this paper. Further, we use the expressions to obtain simple procedures that provide the RMA values required to achieve a target set of BER-s for a specified signal-to-noise ratio. The results of this paper indicate how differentiated QoS may be provided while maintaining high spectral efficiency. R. M. Karthik is currently a Ph.D. candidate in the Centre for Electronics Design and Technology, Indian Institute of Science, Bangalore, India. He received his B. E. (Electronics and Communication Engineering) from Government College of Technology, Coimbatore, India in 1998 and M. E. (Applied Electronics) from College of Engineering, Guindy, Anna University, India in 2000. His current research interests include communication networks and QoS in UMTS Networks. Joy Kuri has a B.E. in Electronics and Telecommunication engineering from Jadavpur University, Kolkata. After a year in the industry, he joined the M.E. program in the Department of Electrical Communication Engineering at the Indian Institute of Science. He went on to receive a Ph.D. from the same department at IISc in 1995. Subsequently, he spent two years at Ecole Polytechnique, University of Montreal, Canada and one and a half years in INRS-Telecommunications, University of Quebec, Canada as a Research Associate. Since 1999 he has been with the Centre for Electronics Design and Technology, Indian Institute of Science, where he is currently Associate Professor. His research and teaching interests are in the areas of modelling, analysis and control of communication networks and stochastic systems. He is co-author of the book Communication Networking: An Analytical Approach by Kumar, Manjunath and Kuri, published by Morgan Kaufman/Elsevier.     

用于超宽带接收机的高速低复杂度模拟自动增益控制环路

在射频接收机中,自动增益控制环路(AGC)根据接收信号幅度控制放大器增益,向后级模数转换器(ADC)提供恒定幅度的信号,以实现不同强度信号的正确接收。在超宽带(UWB)接收机中,极大的信号带宽给AGC的设计提出了挑战。本文提出了一个用于超宽带(UWB)接收机的模拟自动增益控制环路(AGC)。该AGC环路采用多级可变增益放大器(VGA)串联的放大器结构,通过峰值检测电路和模值运算电路检测输出复信号模值的峰值,和参考电位比较后反馈控制VGA的增益,从而得到恒定幅值的ADC的输入。整个电路结构简单,复杂度低。基于HJ0.18μmCMOS工艺的仿真结果表明,本文提出的AGC工作在500MHz带宽下,增益调节范围达40dB,三阶交调点为20dBm,能够满足UWB接收机的要求。     

Improved four-channel direct-conversion SiGe receiver IC for UMTS base stations

This work presents the design and measurement results of an improved four-channel, direct down conversion receiver (DCR) for the application in universal mobile telecommunications system base stations. The whole analog receiver functionality including low noise amplifier, variable gain amplifier, local oscillator frequency divider, in-phase and quadrature DCR mixers and seventh-order active lowpass filter is integrated using Atmel's 50-GHz f/sub t/, 50-GHz f/sub max/ SiGe foundry technology (Atmel, 1998). Important cascaded design parameters of the fully ESD-protected device are a noise figure 1.5 to 2 dB; IIP3 (third-order intercept point) -20.3 to -15.8 dBm and a voltage gain of 51 to 57 dB into a 1000-/spl Omega/ /spl par/ 2.5-pF differential load [analog to digital converter].     

Low cost MMSE algorithm for UTRA TDD mode downlink receiver

A low cost receiver algorithm is presented for the downlink in the emerging third generation mobile radio system time division duplexed mode. The receiver implements a minimum mean square error process at the same cost as a matched filter. This simplifies handset design and allows the network maximum flexibility in allocating timeslots and code channels