Sectoring of a Locally Centralized Communication System in an Indoor Environment

1. Sectoring of a Locally Centralized Communication System in an Indoor Environment Stefan Pettersson Royal Institute of Technology Dept. of Signals, Sensors and Systems

2. Local Centralization • Internal Radio Resource Management • Centralized • Synchronized • “Cheap” signaling • External Radio Resource Management • Distributed • Unsynchronized • “Expensive” signaling CU Central Unit RAU Remote Antenna Unit

3. The Link Gain Matrix Every RAU transmits an ID on a unique beacon channel for the terminals to measure on

4. Internal Radio Resource Management Feasibility Check: Power Control: RAU Selection: Lowest path loss (strongest) Channel Selection: Random The feasibility check is performed prior to a new allocation to ensure the quality of all users. A channel is feasible if the user SIR is above the SIR-target i.e. i  0. The power control balances all SIR in the controlled system

5. Sectoring • Reduced co-channel interference • Trunking loss No frequency reuse between sectors The gray area represents the same channel group

6. Antenna Pattern Constant antenna gain in front and back lobes The number of available channels are split equally between the sectors Front-to-Back Ratio is 15 dB One sector pattern out of four in a four-sector scenario.

7. Indoor Scenario- Building Layout 3 Meters The RAUs are placed at the ceiling level and the terminals at 1.5 meters

8. Indoor Scenario cont.- Floor Layout Meters The Remote Antenna Units are placed in the center of every second office 85% of the terminals are located in the offices and 15% in the corridors

9. Numerical Analysis Snapshot simulations in downlink Lpath [dB] = 37+30log(R)+18.3n((n+2)/(n+1) - 0.46) Log-normal shadow fading with 12 dB std. dev. PC dynamic range is 30 dB Orthogonal channels All channels are available at every RAU No mobility n = Tx-Rx distance in # of floors

10. Definitions • Performance measures: • assignment failure rate, nu - The fraction of users that did not get a feasible channel or got a channel that had to low quality • flops per allocation attempt - The number of floating point operations needed for an allocation (Matlab) • CDF of the transmitter powers - The Cumulative Distribution Function = Probability [ P p ] • Relative traffic load = users/channel/cell • Capacity (*) is the load where nu equals 2%

11. Capacity for Different Number of Sectors in a Single CU System The capacity increases from 0.5 to 0.65 with two-sector antennas compared with omni-directional antennas Assignment failure rate Relative traffic load

12. CDF of TX-Power in aSingle CU System Reduced co-channel interference reduces the Tx-powers. Close to 90% of the users transmit with minimum power with twelve-sector antennas. Without sector antennas this number is 30%. Probability Transmitter Power [dBm] at load 0.6

13. Complexity Comparison in a Single CU System The complexity is reduced with sector antennas. The number of co-channel users are smaller making the feasibility check less complex to perform with sectoring. Flops per allocation attempt Relative traffic load

14. Capacity Comparison in aDouble CU System The capacity drops from 0.50 to 0.12 without sector antennas when two controllers cover the building floor. With six-sector antennas, the capacity improves from 0.12 to 0.46. The trunking loss is to large with twelve sectors for further improvement. Assignment failure rate Relative traffic load

15. CDF of SIR for a Double CU System A channel is feasible if the Signal-to-Interference Ratio is above 9 dB. For twelve sectors, the probability is below 2·10-3 of having a SIR less than 9 dB. The assignment failure at load 0.4 is more than 2·10-2. The difference is lack of channels to assign i.e. trunking losses occur. Probability SIR [dB] at load 0.40

16. Complexity Comparison in a Double CU System The complexity is similar for different number of sectors at low loads. A feasible channel is often found at the first attempt at low loads and the overhead is the same for all sector scenarios Flops per allocation attempt Relative traffic load

17. Definition of Gc and Lk • Capacity Gain is the capacity for a system divided by the capacity for a single-CU, single-sector (omni) system • Complexity Reduction is the quotient between the number of flops for a single-CU, single-sector system (1,1) and the number of flops for the system at the loads where the assignment failure is 0.02.

18. Capacity Gain and Complexity Reduction for a Single CU System One Central Unit covers the whole floor The assignment failure rate is maintained at two percent

19. Capacity Gain and Complexity Reduction for a Double CU System Two Central Units cover half the floor each The assignment failure rate is maintained at two percent

20. Conclusions Sector antennas improve the capacity and reduce the complexity of the studied communication system Local centralization reduces the complexity but also the capacity The capacity loss using multiple controllers can be regained with sectoring More sectors result in lower transmitter powers thus improving the coexisting capability of multiple systems