Application in Shanghai FuTURE 4G TDD Experiment Network

The simplified form of soft fractional frequency reuse scheme has been applied in the 4G TDD experimental network in Shanghai successfully. As shown in Figure 3, there are two Access Points (AP), namely AP1 and AP2, in the experimental network. The distributed antenna arrays at the lecture theatre and the Golden Sun connect to AP1; the distributed antenna arrays at the small hotel and the library connect to AP2. Each site has four antennas. In Figure 3, the region circled by the blue line represents Cell 1, and that circled by the green line represents Cell 2.



The soft fractional frequency reuse scheme with two cells is applied in Shanghai 4G experimental network. Its results are as follows:

(1) When there is only user, MT1, in Cell 1, MT1 will use the whole spectral resources in Cell 1, and the rate can reach 100 Mb/s.

(2) When there are two users, MT1 and MT2, in Cell 1, each user uses half of the frequency resource, enjoying the highest rate of 50 Mb/s.

(3) When MT1 and MT2 move inside Cell 1, each user uses half of the frequency resource, and can also get the highest rate of 50 Mb/s.

(4) When MT2 in Cell 1 moves to the handover region, but maintains the connection with Cell 1, MT1 and MT2 respectively use half of the frequency resource of Cell 1, enjoying the highest rate of 50 Mb/s.

(5) When MT2 moves to the handover region, and connects with Cell 2, MT1 uses half of the frequency resource of Cell 1, and MT2 uses the half resource of Cell 2. Each user enjoys the highest rate of 50 Mb/s, and the frequency reuse factor is 0.5.

(6) When MT1 in Cell 1 and MT2 in Cell 2 move to appropriate positions, (for example, MT1 is near the lecture theatre, while MT2 moves to the library), the two users enjoy the total frequency resources in both Cells 1 and 2, and can get the highest rate of 100 Mb/s. The frequency reuse factor is 1.

 Conclusions
This paper proposes a soft fractional frequency reuse scheme in order to meet the requirements of improving spectral efficiency and intra-frequency network in 4G mobile communication systems. The scheme has three forms for implementation, and a proper form may be selected according to the link gain of the physical layer in practical applications. The soft fractional frequency reuse scheme has been simply applied in Shanghai FuTURE 4G TDD experimental network, with a successful result. The studies show that the system frequency reuse factor can be up to 1/3-1 when adopting the soft fractional frequency reuse scheme, which provides a good solution to improving intra-frequency network and frequency utilization.