Factors Affecting Throughput in LTE :- Low mcs, Low sinr, Low rsrq , high prb usage, wrong earfcn Definition, no Carrier aggregation ör missing ca configuration, Pci , Route sequence index collision, Wrong tac planning, gateway security problem, etc. air quality (now sinr, rsrq, etc etc), modulation level. For example, 16QAM, 64QAM, etc. Low Throughput Issue:- 1 - Poor coverage (BLER) 2 - Availability issue 3 - Uplink Interference 4 - A poor RACH decoding SR 5 - High error on S1 link. 6 - Delay on S1 link towards MME & SGW. 7 - Accessibility issue. 8 - Handover failure. 9 - Lack of PRBs. 10 - Problematic UE. 11 - Downlink Interference (Bad CQI) 12 - MIMO Parameters 13 - High VSWR 14 - High radio errors or instability issue. 15 - Maximum number of RRC connections active per cell 16 - Maximum number of users per TTI supported per cell. 17 - Core network, MME/SGW, etc 18 - Transmission instability & bottleneck. 19 - Incorrect parameter setting. 20 - Badly tuned handover parameters...
Introduction To Cellular Communication
To provide wireless communication access to subscribers we need a pair of RF channels per active call. In a large city with several thousand subscribers number of channels required would be so large that they cannot be accommodated on one site. Also there is a limit to availability of spectrum. If an operators get a 5 MHz band, then he has only 25 channels to use with 25 channels loaded at one site he can offer cellular service to 2000 subscribers at most. To overcome this limitation, you have to create zones of coverage, which are called as cells.
Cellular Structure
Cells in cellular system are hexagons. The actual cell covered by a base station takes a very different shape depending upon the terrain obstructions and transmitting antenna characteristics. The cells are of different sizes and shapes to cover a den sly populated area, smaller cells are used. Where a large cells cover a low subscriber density areas. On the highways and main roads cell size is optimised to cover larger length of the cell along the road. This is made possible by using directive antenna.
Code Division Multiplexing Access:-
The CDMA standard allows up to 61 simultaneous users in one 1.2288 MHz channel. By processing each voice packet with two PN codes. It is virtually impossible to monitor a CDMA conversation or fraudulently access ESNs, PINs or credit card numbers.
Though there are 64 Walsh codes available to differentiate call and theoretical limits are around 40 calls. The operational limitations and quality issues will reduce the maximum number of calls somewhat below this value.
Channelization Methods
- The band used in CDMA is 824 MHz to 894 MHz (50 MHz + 20 MHz separation)
- Frequency channel is divided into code channels
- 1.25 MHz of FDMA channel is divided into 64 code channels.
CDMA is a Code Division Multiple Access
- Spread spectrum technique
- Multiple users share the same frequency in one cell
- Same frequency in all the cells
- Takes advantage of Multipath
- Capacity is soft
- Operates under presence of interference
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