Influence of Smart Antenna on Radio Resource Management

The beamforming of smart antenna effectively reduces the interference between users, and its essence is to distinguish the signals of different users in space. If DCA can assign users in the same direction to different time slots as far as possible and users in the same time slot to different directions, it can give full play to the space division effect of smart antenna and minimize multiple access interference. In order to achieve this goal, it is necessary to increase the function of DCA(dynamicchannellocation) to acquire and process user space information.

Smart antenna can estimate the direction of signal (DOA), and DCA can allocate time slots for new users according to their positions in each time slot, so as to minimize the multiple access interference in the user beam. In figs. 4(a) and 4 (b), the new user (terminal 3) has no beam overlap in time slot 2, so it should be given priority.

Fig. 4 is a schematic diagram of allocating user positions according to the size of time slot interference.

In order to increase the ability of DCA algorithm to allocate space resources, we must first obtain the user's position information and measure the interference of directional beam according to the user's position. In this way, in DCA algorithm, the time slot can still be selected according to the interference of new users in different time slots, which refers to the interference in the direction of users, not the interference generated by users in the whole cell in this time slot. The baseband processing process of smart antenna combined with joint detection is shown in Figure 5.

In fig. 5, the data output by generating system matrix A is equalized and filtered in the spatial domain, from which intra-beam interference can be calculated as the basis of time slot allocation in DCA. The calculation method of interference needs further study, so that it can correctly reflect the size of interference in the equivalent baseband beam.

Fig. 5 is a schematic diagram of baseband signal processing combining smart antenna technology and joint detection technology.

The ideal goal of smart antenna is to realize space division multiplexing (SDM). When the beamforming effect is good enough, users in different directions can be assigned the same code channel (carrier, time slot and spreading code are all the same), which will increase the system capacity exponentially. Considering the mobility of users, the change of relative position between users may make the user access to time division multiplexing scheme invalid, that is, there will be greater co-frequency interference. Code channel adjustment in fast DCA can overcome this problem. When DCA knows that the user's co-frequency interference is greater than the threshold, it will trigger channel adjustment and allocate new code channel resources for users with serious co-frequency interference to eliminate the interference. Smart antenna combined with DCA is an effective way to realize space division multiplexing.

2. The influence of smart antenna on power control

The influence of smart antenna on power control is shown in the following aspects.

(1) Change the flow of power control. When there is no smart antenna, the power control is adjusted periodically according to the SIR measurement value and the target value. When there is a smart antenna, first aim the main beam at the user to be adjusted, and then make relevant measurements.

(2) The requirements for power control are reduced. In the case of smart antenna, when the main beam is aimed at the user, the transmission power of the user terminal can be greatly reduced compared with the case without smart antenna because of the high antenna gain.

(3) In the case of smart antenna, the balance equation of power control becomes complicated. The traditional power control modeling method is no longer applicable. The power control algorithm model in this case is related to the specific smart antenna algorithm.

3. The influence of smart antenna on packet scheduling

The function of packet scheduling algorithm is to improve users' ability to use air interface resources when distributing packet data services among packet users. The packet scheduling used in practical systems is a combination of time division and code division. However, after smart antenna is introduced, beam resources are introduced, thus one-dimensional space division is added to the packet scheduling method. The available resource model of air interface has changed, so the algorithm model must also be changed. Using beam resources, the multiple access interference between users is reduced by space division, and the transmission rate of grouped users is improved. At the same time, using smart antenna to locate UE can optimize the scheduling rate of users according to the location information, thus making more effective use of system resources.

4. The influence of smart antenna on switch control

Using smart antenna technology will inevitably involve some network performance, such as user mobility management. At the same time, the user's spatial location has become a new available physical wireless resource in the mobile communication system, which includes four-dimensional elements of frequency, time slot, code channel and spatial angle. This brings great flexibility to admission control and resource reservation in the handover process. In addition, smart antenna can provide some useful location reference information for handover, improve system resource utilization, shorten handover time, reduce call drop rate, reduce signaling interaction and improve handover success rate.

Smart antenna not only brings the above benefits to system switching, but also increases the complexity, uncertainty and instability of switching. For example, in the process of physical channel allocation, when there is a conflict and channel adjustment and switching is needed, the switching algorithm used is more complicated than that with only three resources, and the switching management of mobile users is also much more complicated. The use of smart antenna also makes the relationship between some criteria in the handover algorithm blurred and complicated, and there are many random factors in parameter measurement, such as the position of mobile users and the effect of smart antenna. The respiratory effects of the cell is more randomized, so is the handover area.