Presentation for CannesExpoExample: In GSM, the cell capacity (channel number) is fixed.
CDMA system:
soft capacity
Hard capacity
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CAC: Call Admission Control
Used to admit/reject the resource request to keep the system work in stable state.
Load Balance:
To balance load between cells to maximize the system capacity
Congestion Control:
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How the CAC been implemented.
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Why we need CAC?
WCDMA is an interference limited system, after a new call is admitted, the system load will be increased.
If a cell is high loaded, a new call will cause ongoing user dropped.
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New call
Bandwidth increasing reconfiguration
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Downlink : TCP (Transmitted Carrier Power)
The RTWP has an unique corresponding with the uplink load
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Activity factor
Activity factor : The percentage of time that the data transmission is active.
The UL and DL activity factor may be different for dedicated channel.
Different service type has different activity factor.
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Eb/No
UL load factor
Noise rise & UL load factor
Noise rise : defined as the ratio of RTWP and background noise.
Relationship between UL load factor and the noise rise.
and
Received power if there is no interference.
Increment due to the interference.
Meaning of the UL load factor
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Eb/No
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Definition of DL load factor
Let’s suppose for simply, and base on , we can get
Defined as the DL load factor
Base power due to the pass loss.
Increment due to the interference.
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Non-orthogonal factor and interference from other cells are various with position, and are difficult to measure.
The same DL load factor may correspond to different transmitted carrier power due to the different pass loss (cell radius).
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Strategies
Only for dedicated channels, and reserve a certain resource for the common channels.
UL and DL CAC algorithms are independently.
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Strategies
Handover threshold, conversational threshold and other services threshold are used to keep the priority of the handover higher than the conversational, conversational than the Best Effort services.
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Reference service : 12.2k AMR with activity factor = 1.
Normalized traffic factor(NTF) has the meaning of equivalent number of user i relatives to the 12.2k AMR.
UL and DL may have different normalized traffic factor.
No resource is reserved for common channels.
Normalized traffic factor of user i :
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Selected by algorithm switch
Auto switch from algorithm 1 to algorithm 2 when algorithm1 is selected for UL/DL.
When RTWP and/or TCP measurement value are/is invalid/unavailable, the CAC will change from algorithm 1 to 2 automatically.
When measurement are/is valid/available, the CAC will change back to algorithm 1 automatically.
UL and DL are independently.
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How the LDB been implemented.
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Original
Result
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Intra-frequency LDB
Inter-frequency LDB
To move calls in a heavily loaded cell to neighboring cells.
To relieve calls in surrounding cells when lightly loaded.
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How to select user?
Compute the normalized traffic factor (NTF) for each of the UEs belongs to the Maximum Transmitted Carrier Power carrier.
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Why We Need Congestion Control ?
To receive information correctly, signal in receiver must be above certain S/I (Signal/Interference ) threshold.
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Why We Need Congestion Control ?
To overcome the interference, transmitter must increase signal power, that is, it need more MS or BTS power.
MS or BTS power is limited. If interference keeps rising, S/I requirement can not be achieved at a certain degree, quality of services will deteriorate and some users will drop.
Congestion occurs.
Why We Need Congestion Control ?
To guarantee the network’s stability and customers’ QoS (Quality of Service), we should try our best to avoid congestion.
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Object: All BE (Best Effort) services.
Range: Downlink only. (Optimization is ongoing.)
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Congestion Control Description
LCC will monitor the cell’s downlink transmission carrier power periodically or by event. When LCC finds the cell’s downlink load rises above a certain threshold or receives a event claiming congestion, it will inform MAC layer to limit the maximum Transport Format(TF) of the BE service to a small value in order to quickly pull down the bit-rate.
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Congestion Control Example
For a 144kbps background user: TB size is 336bits, max valid TF number is 9.
When congestion is detected, MAC will compute: 9*50%≈4, so the adjusted max valid TF number is 4. The bandwidth halves. Note: 50% is a parameter named Adjust Coefficient.
MAC starts a Adjust Timer, and then computes at the timer’s expiry: 4*50%≈2, so the adjusted max valid TF number is 2.
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Congestion Control Example
When congestion relieves, MAC will be informed. So MAC will begin recovering process.
Recovering Process: Assumed that the user’s max valid TF number has been reduced to 1 during the congestion. MAC first computes: 1+1=2. So the recovered max valid TF number is 2. Note: 2 should be in the TFS which MAC can use.
Then MAC starts a recovery timer, if it expires, MAC increase the max valid TF number from 2 to 3……
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current load factor.
estimate the increment of load factor.
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handover to the lowest