1. Royal Institute of Technology Dept. of Signals, Sensors and Systems
Sectoring of a Locally Centralized Communication System in an Indoor Environment
Stefan Pettersson
Royal Institute of Technology
Dept. of Signals, Sensors and Systems
12/3/2018

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
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3. The Link Gain Matrix
Every RAU transmits an ID on a unique beacon channel for the terminals to measure on
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4. Internal Radio Resource Management
RAU Selection: Lowest path loss (strongest)
Channel Selection: Random
Feasibility Check:
Power Control:
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
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5. Sectoring Reduced co-channel interference Trunking loss
No frequency reuse
between sectors
The gray area represents the same channel group
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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.
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7. Indoor Scenario - Building Layout
3 Meters
The RAUs are placed at the ceiling level and the terminals at 1.5 meters
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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
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9. Numerical Analysis Snapshot simulations in downlink
Lpath [dB] = 37+30log(R)+18.3n((n+2)/(n+1) )
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
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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%
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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
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12. CDF of TX-Power in a Single 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
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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
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14. Capacity Comparison in a Double 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
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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
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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
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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.
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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
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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
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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
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