Digital Trunking Communication Network And Multiple Antennas Technology

Though not as popular as public cellular mobile systems, trunking communication networks i.e. private mobile radio (PMR) networks provide services for a wide variety of professional users in several sectors, including public safety (e.g., police, fire departments, ambulances), transport (railways, buses, taxis, etc) and other utilities (water, electricity, gas, coal, etc). With the development of tech-nology, the trend of next generation digital trunking communications is broadband and customization service, such as public safety system for emergency response, commanding and dispatching system with different user priorities, real-time video surveillance system and so on. At present, the main problem of second genera-tion digital trunking communications is their inability to satisfy the multimedia service with high data rate. In order to solve such problems, a new digital trunk-ing communication networks is needed. The use of multiple antennas for wireless communication systems, which can push the capacity and throughput limits as high as possible without an increase in spectrum bandwidth, has gained overwhelming interest both in academia and industry. It is divided into smart antenna and Mul-tiple Input Multiple Output (MIMO) technology according to the different signal processing. Distributed antennas is one of the main construction of future multiple antennas system, which can obtain good wireless coverage performance. The paper lays its point on distributed network architecture of next generation digital trunking communications, multiple antennas technology in Point-to-Multipoint communica-tions and distributed antennas in high-speed railway digital mobile communication system. Primary contents and innovations are listed as bellows:(1) Based on the development of wireless communications, the distributed network architecture of digital trunking communications is proposed, and its new characteristics are analyzed. Next generation digital trunking communications will trend to broadband, flexible, customization service and all-IP networks. With the distributed network architecture, it is flexible to construct the high-efficiency and high data rate wireless networks quickly, has strong ability of self-healing with Ad hoc and Mesh network. The all-IP architecture, with different access options seamlessly integrated with an IP packet network layer, allows all communication services to be carried over a single network infrastructure. Besides, several emerging technologies related to next generation digital trunking communications are also discussed, such as multiple antennas technology, multicast communication, signaling optimization with shorter system connecting time, i.e. call-setup time, cognitive radio, cooperative relay technology, carrier aggregation and Cross Layer Design.(2) Two angle based multicast transmit beamforming algorithms and two lo-cation based multicast transmit beamforming algorithms are proposed in Multicast communication, which is one of the main feature service in digital trunking com-munications. The user’s full channel state information (CSI) could not be known by base station in time, so the angles between the users and the reference plane of the smart antenna can still be used in multicast transmit beamforming. Two angle based multicast transmit beamforming algorithms under single-group scenar-ios are proposed:Maximize Average Beamforming Gain (MABG) algorithm and Maximize Minimum Beamforming Gain (MMBG) algorithm. The simulation re-sults show that the angle based algorithms can improve the signal quality with4dB effectively than omni-directional antenna. Tne MMBG algorithm performances good in all average signal to noise ratio (SNR), minimum SNR, average of beam-forming gain and minimum beamforming gain. It gives a good tradeoff in fairness and effectiveness. Taking it further, the distance information is plused on angle based algorithm, two location based multicast transmit beamforming algorithms are proposed, in which both MABG and MMBG are the goal constraint to subject too. The location based MMBG algorithm’ beamforming directional diagram fit the distribution of users very well, both in angles and distance. Besides, distribu-tion of users, the number of array antennas, the number of user-clusters and other influencers are discussed.(3) Base on analysis of E-MBMS (Enhanced MBMS), a group based adaptive MIMO scheme in multicast communications is presented and analyzed. Both spatial multiplexing and diversity techniques are focused on. The concept of group based multicasting is used, all users are formed into two groups based on the different users’ distributions. Spatial diversity technique is used to enhance signal strength of the cell edge users’ group; and spatial multiplexing technique is used to increase the data rate of the other group. The choosing MIMO technology for a single user according to its distance from Base station is analyzed first. Spatial boundary dBoundary and Boundary factor λ are calculated. Then3Group-formed rules are proposed by Spatial boundary dBoundary, Boundary factor λ and user’s average distance. The group based adaptive MIMO technology in multicast communications can improve the the marginal users performance, which is the big problem for multicast wireless mobile communications. On the other hand, it also increase the effectiveness of multicast communications by using spatial multiplexing.(4) Distributed antennas, one of the construction of future multiple anten- nas system is introduced and fixed handover cell with dual-antenna for high-speed railway Distribution Antennas System (DAS) is proposed to solve the problem of fast handover in the traditional cellular network. The main obstacles in high-speed railway communications are analyzed. Both traditional DAS and improved DAS are analyzed and compared with the system without distributed antennas in high-speed railway digital mobile communication system. Coverage area, overlap area, frequency division multiplexing, handover time and handover frequency are analyzed in different systems respectively. There is sufficient time to complete the handover in Fixed Handover Cell. It can effectively avoid the occurrence of a ping-pong ef-fect. Its advantages include seamless handover, simple handover, and cost-effective deployment to support high mobility. Generally, all the performance in DAS are much better than the system without DAS, but the improved DAS is a little decrease than the traditional DAS because the Fixed Handover Cell between the Logical Cells contains two Remote Antenna Units (RAUs).