Top Banner
Performance Evaluation of CDMA Networks Mid-Term Presentation Rahul Kumar
31
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript

Mid-Term Presentation Rahul Kumar

Forward & Reverse Channels

Walsh Codesy Walsh codes are used to identify users on the forward link. y Hadamard Matrices are used to generate Walsh Codes

y There are 64 different sequences in the Walsh Code and each sequence

is 64 chips long. Some of these codes are used for setting up the channels and the rest are used for the transmission of the data.y All Walsh codes are mutually orthogonal and this means that the

correlation of two codes results in 32 1 s and 32 0 s.

Pilot Channel: Walsh Code 0 The Pilot is a structural beacon which does not contain a character stream. It is used as a timing source in system acquisition and as a measurement devise during handoffs. It allows the mobile stations to acquire the timing of the forward channel and serves as a phase reference for demodulation. It allows the mobile to search out the best base station for acquisition & hand off. SYNC Channel: Walsh Code 32 This carries a data stream of system identification and parameter information used by mobiles during system acquisition. Paging Channel: Walsh Codes 1 up to 7 There can be from one to seven paging channels as determined by capacity needs. They carry pages, system parameters, information and call set up orders. Traffic Channels: Remaining Walsh Codes The Traffic channels are assigned to individual users to carry call traffic. All the remaining Walsh codes are available for user traffic.

Short PN Codey Consists of two PN sequences Q & I and each sequence

is 32,768 chips long.y Each sequence is generated in similar but differently

tapped 15 bit linear feedback shift registers.y Both of these sequences are used together modulating

the two phase axes of a QPSK modulator.

Long PN Codey This code is generated in a 42 bit register, and is more

than 40 days long and hence is generated chip by chip.y Each handset codes its signal with the PN Long Code

but at a unique offset computed using its ESN(32 bits) and 10 bits set by the system.

Important Termsy Rake Receiver- It is an integral part of the CDMA handset and has

three traffic co-relators which independently recover a particular PN offset and Walsh Code. Each of the fingers can be targeted on delayed multipath reflections, or even on different BTSs. energy of the desired pilot alone to the total energy received. It foretells the readability of the associated traffic channels. It never appears higher than Pilot s percentage of serving cell s transmitted energy. parameters. It characterizes the received quality data packets (frames). The value should not exceed 6. If FER is good then for the moment you don t need to be concerned about the other parameters.

y Energy to Interference density Ratio (Ec/Io)- This is the ratio of the

y Frame Erasure Rate (FER) - Probably the most important of all the

What happens when your mobile is moving around?

Handoff is a very essential component for dealing with the mobility of end users. It ensures the continuity of wireless services when the mobile user moves across the cell coverage boundaries. When a MS is moving from coverage of one sector to another sector (same or different BTS) and signal strength serving the MS becomes weak , Handoff to new sector with strong signal strength happens

Types of Handoff

Soft Handoff: A mobile simultaneously maintains connection with two or three base stations.

Softer handoff. This type of handoff occurs when a mobile transitions between two different sectors of the same cell.

Handoff Process

Power ControlPower control is essential to the smooth operation a CDMA system. Because all users share the same RF band through the use of PN codes, each user looks like random noise to other users. The power of each individual user, therefore, must be carefully controlled so that no one user is unnecessarily interfering with others who are sharing the same band. So what power does a mobile initially transmit with? 1. Initial Transmit Power is High 2. Initial Transmit Power is Low

Access Probes

pt , initial = -pr - 73 + NOM_PWR + INIT_PWR

Call Processing States

Making an Outgoing Call

Receiving an incoming call

Network PlanningRF planning y The goal is to achieve optimum use of the resources and maximum revenue potential whilst maintaining a high level of system quality. y The designed system should allow capacity to be added economically when traffic demand increases. y By doing proper RF Planning by keeping the future growth plan in mind we can reduce a lot of problems that we encounter in the future and also reduce substantially the cost of optimization.

PN Offset PlanningShort PN Sequences y Each short PN sequence is generated using a shift register with 15 delay elements. The length of such a PN sequence is 32,768 chips.y If a PN sequence is shifted by one chip, then effectively a different PN

sequence is generated.

y In order to provide more isolation among PN sequences that can be

assigned, the IS-95 standard specifies that usable PN sequences need to have a minimum separation of 64 chips between each other. usable PN sequences becomes

y By specifying a minimum separation of 64 chips, the total number of

Frequency Reuse FactorIn terms of interference contributions, the loading factor can be defined as for the home base station

Where is the loading factor. In terms of interference contributions, the loading factor for the home base station can be defined as

where I 't is the interference loading of traffic channels from mobiles that are in other cells, and I m ' is the interference loading of traffic channels from mobiles that are in the home cell.

Map of Drive Test Area

Ec/Io for PN 75

Ec/Io for PN 306

PN 75 is the best PN in this region

PN 306 is the best PN in this region

Forward Channel FER Values

RX Level

TX Level

Case Study 1

Case Study 2

Case Study 3

1.Install a new sector on the sites BTS [1][48] and BTS [1][257] with 30-40 horizontal bandwidth antenna to share the load of the other sectors. 2. Decrease the BTS [1][78] (PN=375) antenna height. The antenna should also be down-tilted.

BTS Sites in Manipal