Study On The Dynamic Channel Allocation Technology In TD-SCDMA System

1. IntroductionTD-SCDMA, the third generation mobile communication standard that China puts forward and holds the independent intellectual property rights, is one of the three primary standards certificated by ITU. The state gradually increases the investment to TD-SCDMA and builds scaled testing net in Qingdao, Xiamen, and Baoding etc. With the united disposal of the Ministry of Information Industry and the testers' unremitting effort, the project goes well as a whole. The encouragement of the policy will truly have a tremendous promoting effect on the development of the whole industrial, and the study on TD-SCDMA has been a hotspot in the communication field. However, the present study and exploiture to TD-SCDMA is roughly limited relative to WCDMA and CDMA 2000. TD-SCDMA is put forward in China, both the international and domestic research to it is seriously lack, so its study must be inhanced further more to insure the success. In order to allocate resources to integrated service, which including voice service—real time service (RT) and data service—non-real time service(NRT), TD-SCDMA, one of the 3G standards, need to be able to afford an efficient resource-allocating mode .As one of the key technic of TD-SCDMA, DCA is very important for TD-SCDMA system.Studying on the DCA algorithmic has been a hotspot in the radio communication research field, the importance is widely acknowledged in the field.After the study on the domestic and overseas'DCA algorithmic, the strategy in the DCA process of TD-SCDMA system has been studied and a mixed-data rate, small grouping borrowed MB DCA scheme is introduced in this paper.Usually the DCA can be divided into Slow-DCA and Fast-DCA.The Slow-DCA scheme is used to allocate and adjust radio resource for every cell in order to confirm the proportion between uplink (UL) and downlink (DL).The Fast-DCA scheme is used to allocate radio resource for the user applying for connection and adjust the resource based on system state. 2. Slow-DCA scheme in TD-SCDMA systemSlow-DCA scheme is used to confirm the proportion between UL and DL, an UL/DL dynamic time slots allocation strategy is proposed to match the load in UL/DL. Slow-DCA is implemented in every period of time'T'to adapting the mutative portfolio in UL/DL.'T'can be confirmed by the complexion of mutative portfolio.The time slots allocation arithmetic of single cell condition is proposed in this paper. When the time slots allocation is needed, the required time slots of voice service is confirmed by quantity of the on-line User firstly, then the residuary time slots can be allocated by the condition of date service in UL/DL. Since proportion between the time slots and portfolio matches is almost the same, the capability losing costed by the limited of unilateralism resource is less and the service transmission adaptability will be better, the proportion of time slots in UL/DL and the switching point can be confirmed.3. Fast-DCA scheme in TD-SCDMA systemAccording to the UL/DL time slots rate that confirmed by Slow-DCA arithmetic, Fast-DCA arithmetic gains the usable resource list of the data service and the voice service. Fast-DCA allocates the resource for voice call applying for access and data packets waiting for transmitting. The movable boundary (MB) scheme is adopted when allocating the usable resource. The scheme divides the channel into two parts: data service channel and voice service channel. If the voice service channel is free and the data buffer-queue is not empty, the data service will be transmitted through the voice service channel. When a new voice call arrives and the voice service channel is not free, the voice call will grab the voice service channel which was borrowed by data service.The paper improves on the movable boundary DCA (MB DCA) scheme which is proposed by reference [51] and proposes a MB DCA improved scheme which is intitule the mixed-data rate, small grouping borrowed MB DCA scheme. If the free BRU of voice service time slots are between 8 and 16, it can be borrowed to date service at the rate of 64kbps; If the free BRU of voice service time slots are out of 16, it can be borrowed to date service at the rate of 144kbps or two separate data service at the rate of 64kbps. In order to analyze the improved MB DCA scheme, a planar Markov model is founded to analyze and simulate on computer.The fixed boundary DCA (FB DCA) scheme, the MB DCA scheme and the mixed-data rate, small grouping borrowed MB DCA scheme are analyzed under the condition of symmetrical time slots. At office area, where data service is primary, the MB DCA improved scheme under the condition of symmetrical time slots will be limited by DL resource and produce capability loss. The MB DCA improved scheme under the condition of asymmetrical time slots which can work well is still not reported at present, so this paper studies on the MB DCA improved scheme under the condition of asymmetrical time slots and compares to the MB DCA scheme under the condition of symmetrical time slots.4. The simulation and analysis of the MB DCA improved schemeTo validate the performances of the the mixed-data rate, small grouping borrowed MB DCA scheme, the FB DCA scheme, the MB DCA scheme and the mixed-data rate, small grouping borrowed MB DCA scheme are simulated by computer respectively. These schemes are compared in these aspects of the voice call blocking probability, the average waiting delay of data packet, the data packet dropping probability and the total channel utilization efficiency. The result shows that, compared with the FB DCA scheme and MB DCA scheme, the mixed-data rate, small grouping borrowed MB DCA scheme reduces the average waiting delay of data packet and the packet dropping probability and improves the total channel utilization efficiency without affecting the performance of voice service.The MB DCA improved scheme is also simulated by computer when the time slots proportion of UL/DL is 2:4, the capability index of data service and voice service in UL/DL are gained in the improved MB DCA scheme under the condition of time slots asymmetry between UL and DL and compared to the performance index under the condition of time slots symmetry between UL and DL. The result shows, at the place where the data service occupies the main proportion, the improved MB DCA scheme under the condition of time slots asymmetry between UL and DL takes on better performance. The MB DCA improved scheme of asymmetrical time slots make big improvement on the DL data service performance and the UL data service performance is not influence by and large on this condition.5. ConclusionOn the base of studying on the FB DCA scheme and MB DCA scheme, this paper improves the MB DCA scheme and puts forward a mixed rate, small grouping borrowed MB DCA scheme and analyzes the capability of the MB DCA improved scheme under the condition of asymmetry/symmetry time slots between UL and DL. The result shows that the MB DCA improved scheme takes on better performance. And certain reference is provided for the research on the DCA of TD-SCDMA.