cdma handout for summer trg

8/2/2019 CDMA Handout for Summer Trg

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CDMA Technology

Access Network:

Access network, the network between local exchange and subscriber, in the

Telecom Network accounts for a major portion of resources both in terms of capitaland manpower. So far, the subscriber loop has remained in the domain of the copper

cable providing cost effective solution in past. Quick deployment of subscriber loop,

coverage of inaccessible and remote locations coupled with modern technology have

led to the emergence of new Access Technologies. The various technological options

available are as follows :

1. Multi Access Radio Relay

2. Wireless In Local Loop

3. Fibre In the Local Loop

Wireless in Local Loop (WILL)Fixed Wireless telephony in the subscriber access network also known as Wireless in

Local Loop (WLL) is one of the hottest emerging market segments in global

telecommunications today. WLL is generally used as the last mile solution to deliver

basic phone service expeditiously where none has existed before. Flexibility and

expediency are becoming the key driving factors behind the deployment of WILL.

WLL shall facilitate cordless telephony for residential as well as commercial

complexes where people are highly mobile. It is also used in remote areas where it is

uneconomical to lay cables and for rapid development of telephone services. Thetechnology employed shall depend upon various radio access techniques, like FDMA,

TDMA and CDMA.

Different technologies have been developed by the different countries like CT2 from

France, PHS from Japan, DECT from Europe and DAMPS & CDMA from USA. Let us

discuss CDMA technology in WLL application as it has a potential ability to tolerate a

fair amount of interference as compared to other conventional radios. This leads to a

considerable advantage from a system point of view.

SPREAD SPECTRUM PRINCIPLEOriginally Spread spectrum radio technology was developed for military use to

counter the interference by hostile jamming. The broad spectrum of the transmitted

signal gives rise to Spread Spectrum. A Spread Spectrum signal is generated by

modulating the radio frequency (RF) signal with a code consisting of different pseudo

random binary sequences, which is inherently resistant to noisy signal environment.


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A number of Spread spectrum RF signals thus generated share the same frequency

spectrum and thus the entire bandwidth available in the band is used by each of the

users using same frequency at the same time.

Fig-1 CDMA ACCESS A CONCEPT

On the receive side only the signal energy with the selected binary sequence code is

accepted and original information content (data) is recovered. The other users

signals, whose codes do not match contribute only to the noise and are not

despread back in bandwidth (Ref Fig-1) This transmission and reception of signals

differentiated by codes using the same frequency simultaneously by a number of

users is known as Code Division Multiple Access (CDMA) Technique as opposed to

conventional method of Frequency Division Multiple Access and Time Division MultipleAccess.

In the above figure, it has been tried to explain that how the base band signal of 9.6

Kbps is spread using a Pseudo-random Noise (PN) source to occupy entire bandwidth

of 1.25 Mhz. At the receiving end this signal will have interference from signals of

other users of the same cell, users of different cells and interference from other noise

sources. All these signals get combined with the desired signal but using a correct PN

code the original data can be reproduced back. CDMA channel in the trans and

receive direction is a FDD (Frequency Division Duplexing) channel. The salient

features of a typical CDMA system are as follows:

Frequency of operation: 824-849Mhz and 869-894 Mhz

Duplexing Mehtod: Frequency Division Duplexing (FDD)

Access Channel per carrier: Maximum 61 Channels

RF Spacing: 1.25 Mhz


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Coverage: 5 Km with hand held telephones and approx.

20 Km with fixed units.

The different types of codes used for identification of traffic channels and usersidentification etc as follows:

Different Codes used in CDMA

Walsh Code:

In CDMA the traffic channels are separated by unique Walsh code. All such codesare orthogonal to each other. The individual subscriber can start communicationusing one of these codes. These codes are traffic channel codes and are used fororthogonal spreading of the information in the entire bandwidth. Orthogonalityprovides nearly perfect isolation between the multiple signals transmitted by the basestation.

The basic concept behind creation of the code is as follows:

(a) Repeat the function right

(b) Repeat the function below

(c) Invert function (diagonally)

0 ----- 0 0 -------- 0 0 0 0

0 1 0 1 0 1

0 0 1 1

0 1 1 0

Long Code:

The long pseudo random noise (PN) sequence is based on 242 characteristic

polynomial. With this long code the data in the forward direction (Base to Mobile) is

scrambled. The PN codes are generated using linear shift registers. The long code is

unique for the subscribers and is known as users address mask.

Short Code:

The short pseudo random noise (PN) sequence is based on 215 characteristic

polynomial. This short code differentiates the cells & the sectors in a cell. It also

consists of codes for I & Q channel feeding the modulator.

Advantages: CDMA wireless access provides the following unique advantages.


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Larger Capacity:

Let us discuss this issue with the help of Shannons Theorem. It states that thechannel capacity is related to product of available band width and S/N ratio.

C = W log 2 (1+S/N)

Where C = channel capacity

W = Band width available

S/N = Signal to noise ratio.

It is clear that even if we improve S/N to a great extent the advantage that we areexpected to get in terms of channel capacity will not be proportionally increased. Butinstead if we increase the bandwidth (W), we can achieve more channel capacityeven at a lower S/N. That forms the basis of CDMA approach, wherein increasedchannel capacity is obtained by increasing both W & S/N. The S/N can be increased bydevising proper power control methods.

Vocoder and variable data rates:

As the telephone quality speech is band limited to 4 Khz when it is digitized with PCMits bit rate rises to 64Kb/s vocoding compress it to a lower bit rate to reducebandwidth. The transmitting vocoder takes voice samples and generates an encodedspeech/packet for transmission to the receiving vocoder. The receiving vocoderdecodes the received speech packet into voice samples. One of the important featureof the variable rate vocoder is the use of adaptive threshold to determine therequired data rate. Vocoders are variable rate vocoders. By operating the vocoder athalf rate on some of the frames the capacity of the system can be enhanced withoutnoticeable degradation in the quality of the speech. This phenomenon helps to absorbthe occasional heavy requirement of traffic apart from suppression of backgroundnoise. Thus the capacity advantage makes spread spectrum an ideal choice for use in

areas where the frequency spectrum is congested.Less (Optimum) Power per cell:

Power Control Methods: As we have already seen that in CDMA the entire bandwidthof 1.25Mhz is used by all the subscribers served in that area. Hence they all will betransmitting on the same frequency using the entire bandwidth but separated bydifferent codes. At the receiving end the noise contributed by all the subscribers isadded up. To minimize the level of interfering signals in CDMA, very powerful powercontrol methods have been devised and are listed below:

1. Reserve link open loop power control

2. Reserve link closed loop power control

3. Forward link power control

The objective ofopen loop power control in the reverse link(Mobile to Base) isthat the mobile station should adjust its transmit power according to the changes inits received power from the base. Open loop power control attempts to ensure thatthe received signal strength at the base station from different mobile stations,irrespective of their distances from the base site, should be same.


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In Closed loop power control in reverse link, the base station provides rapidcorrections to the mobile stations open loop estimates to maintain optimum transmitpower by the mobile stations. The base station measures the received signal strengthfrom the mobile connected to it and compares it with a threshold value and a decisionis taken by the base every 1.25 ms to either increase or decrease the power of themobile.

In forward link power control (Base to Mobile) the cell (base) adjusts its power inthe forward link for each subscriber, in response to measurements provided by themobile station so as to provide more power to the mobile who is relatively far awayfrom the base or is in a location experiencing more difficult environment.

These power control methods attempt to have an environment which permits highquality communication (good S/N) and at the same time the interference to othermobile stations sharing the same CDMA channel is minimum. Thus more numbers ofmobile station are able to use the system without degradation in the performance.Apart from the capacity advantage thus gained power control extends the life of thebattery used in portables and minimizes the concern of ill effects of RF radiation onthe human body.

Seamless Hand-off:

CDMA provides soft hand-off feature for the mobile crossing from one cell to anothercell by combining the signals from both the cells in the transition areas. This improvesthe performance of the network at the boundaries of the cells, virtually eliminatingthe dropped calls.

No Frequency Planning:

A CDMA system requires no frequency planning as the adjacent cells use the samecommon frequency. A typical cellular system (with a repetition rate of 7) and a CDMAsystem is shown in the following figures which clearly indicates that in a CDMAnetwork no frequency planning is required.

CDMA Frequency


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Frequency Reuse of 7 in GSM

High Tolerance to Interference:

The primary advantage of spread spectrum is its ability to tolerate a fair amount of

interfering signals as compared to other conventional systems. This factor provides aconsiderable advantage from a system point of view.

Multiple Diversity:

Diversity techniques are often employed to counter the effect of fading. The greaterthe number of diversity techniques employed, the better the performance of thesystem in a difficult propagation environment.

CDMA has a vastly improved performance as it employs all the three diversitytechniques in the form of the following:

A .Frequency Diversity: A wide band RF signal of 1.25 Mhz being used.

B. Space Diversity: Employed by way of multipath rake receiver.

C. Time Diversity:Employed by way of symbol interleaving error detection andcorrection coding.

Capacity Considerations

Let us discuss a typical CDMA wireless in local loop system consisting of a single basestation located at the telephone exchange itself, serving a single cell. In order toincrease the number of subscribers served the cell is further divided into sectors.

These sectors are served by directional antennas.

The capacity of a cellular system is claimed to be 20-40 active lines per sector per1.25 MHz for a single CDMA Radio Channel. In WLL environment assuming an averagebusy hour traffic of 0.1 Erlang, 400 subscribers can be served per sector over a single

1.25 MHz channel.

Assuming typically six sectors in a cell the total capacity of a CDMA networkconsisting of 1.25 MHz duplex channels is 2400 (400x6) subscribers.

Capacity can further be increased if we use another frequency on the same basestation covering the same geographical area (overlapping cell). Thus in 10 Mhz in thebandwidth we can utilize 5 MHz of bandwidth in the forward link and 5 Mhz in thereverse link. Hence if we have 4 RF carriers in 5 Mhz bandwidth, the network cansupport 12000 (5x400x6) subscribers per cell.


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Conclusion

Hence we see that use of common frequency, multipath rake receiver, power control& variable bit rate vocoding and soft hand-off features of CDMA give us the benefitsof no frequency planning, larger capacity, flexibility alongwith high performancequality.

Introduction to CDMA 2000-1X

Network entity description

Base station subsystem (BSS) Base station subsystem is the general termfor the wireless devices and wireless channel control devices that serveone or several cells. Generally, a BSS contains one more base stationcontrollers (BSC) and base transmitter stations (BTS).

RGMTTCPresentation

Um E

Abis A

Q C

B

N H

MS

BT S B SC

PSTNM SC

M S C/SSP VLR

HLR AUCMC

D

MCM

MSS

BSS

Ai

Architecture of CDMA MSC Based WLL system

Mobile switch center (MSC)MSC is a functional entity that performs control and switching to the mobilestations within the area that it serves, and an automatic connecting devicefor the subscriber traffic between the CDMA network and other publicnetworks or other MSCs. MSC is the kernel of the CDMA cellular mobilecommunication system, and it is different from a wired switch in that anMSC must consider the allocation of the wireless resources and the mobility


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of subscribers, and at least it must implement the follows processingactivities:

1. Location Registration processing;

2. Handoff.

Gateway MSC (GMSC)When a non-CDMA subscriber calls a CDMA subscriber, the call will firstbe routed to an MSC, which will inquires the corresponding HLR andfurther route the call to the called partys MSC. This kind of MSC is calledGateway MSC (GMSC). It is up to the network operator to select whichMSCs as GMSCs.

Visitor location register (VLR)

VLR is responsible for the storage and updating of the subscriber data ofmobile stations that roamed to the service area of this VLR. The VLR isgenerally configured together with the MSC. When the mobile stationenters a new location area, the MSC will notice the VLR, which will initiate

registration processing to the HLR to update the subscriber locationinformation. The VLR also stores necessary information for theestablishment of calls in the database for the MSC to search. One VLRcan cover one or more MSC areas.

Home location register (HLR)

The HLR provides subscriber information storage and managementfunctions for the mobile network, including mobile subscribersubscription and cancellation and service authorization and cancellation.At the same time, it helps in the implementation of subscribers call andservice operations. A CDMA can contain one or more HLRs based on thenumber of subscribers, equipment capacity and network organization

mode, with multi-HLR mode realized in the form of virtual HLRs. Thesubscriber information stored in the HLR includes the following two typesin information:

1. Subscription information

2. Subscriber-related information stored in the HLR

Authentication center (AUC)

Authentication center is a function entity for the management ofauthentication information related to the mobile station. It implementmobile subscriber authentication, stores the mobile subscriberauthentication parameters, and is able to generate and transmit the

corresponding authentication parameters based on the request fromMSC/VLR. The authentication parameters in the AUC can be stored in theencrypted form. The authentication center is generally configuredtogether with the HLR. The authentication parameter stored in the AUCinclude:

1. Authentication key (A_KEY);

2. Share secret data (SSD);


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3. Mobile identification number/international mobile subscriber identity(MIN/IMSI);

4. Authentication algorithm (AAV);

5. Accounting (COUNT).

Short message center (MC or SC)

As an independent entity in the CDMA cellular mobile communication

system, the short message center works in coordination with other

entities such as MSC, HLR to implement the reception, storing and

transfer of the short messages from CDMA cellular mobile

communication system subscribers, and store subscriber-related short

message data.

Short message entity (SME)

SME is a function entity for synthesis and analysis of short messages.

Operation and maintenance Center (OMC)

The OMC provides the network operator with network operation and

maintenance services, manages the subscriber information and

implements network planning, to enhance the overall working efficiency

and service quality of the system. There two type of operation and

maintenance centers: OMC-S and OMC-R. An OMC-S is mainly used for

the maintenance work at the mobile switching subsystem (MSS) side; an

OMC-R is mainly used for the maintenance work at the base station

subsystem (BSS) side.

Third Generation Standards

CDMA2000/FDD-MC CDMA2000 using Frequency Division Duplexing-

Multicarrier (FDD-MC) mode. Here multicarrier implies N x 1.25 MHz

channels overlaid on N existing IS-95 carriers or deployed on unoccupied

spectrum.

CDMA2000 includes:1x using a spreading rate of 1.2288 Mcps

3x using a spreading rate of 3 x 1.2288 Mcps or 3.6864 Mcps

1xEV-DO (1x Evolution - Data Optimized)using a spreading rate of

1.2288 Mcps optimized for data WCDMA/FDD-DS Wideband CDMA (WCDMA) Frequency Division

Duplexing-Direct Sequence spreading (FDD-DS) mode. This has a single

5 MHz channel. WCDMA uses a single carrier per channel and employs a

spreading rate of 3.84 Mcps.

UTRA TDD/ TD-SCDMA Universal Mobile Telephone Services

TerrestrialRadio Access (UTRA) and TD-SCDMA. These are Time Division Duplexed


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(TDD) standards aimed primarily at asymmetric services used in unpaired

(i.e., no

separate uplink and downlink) bands. TD-SCDMA is based on a

synchronousTime Division scheme for TDD and wireless local loop applications. The

frameand slot structure are the same as W-CDMA. However, in TDD mode eachslot

can be individually allocated either the uplink or the downlink.

Advantages of CDMA2000:

CDMA2000 is backward compatible with IS-95. Thus a network that is

converted to CDMA2000 from IS-95 will support users with IS-95

handsets. A motivating factor for migration to CDMA2000-enabled

handsets is that it permits use of enhanced data service and

increases the voice capacity of the network. The voice capacityof a CDMA2000 network increases as the percentage of

subscribers with CDMA2000 handsets increases. IS-95 handsets donot contribute to this capacity improvement. It reuses and builds on

the full complement of existing CDMA air interface and network

standards. Both IS-95 and CDMA2000 equipped mobiles can operate

on the same frequency assignment. Existing IS-95 networks can be

converted to CDMA2000 without impact to existing IS-95 PIN

The following are the new additions in CDMA 2000 from IS95.

_ Spreading Rate 1 (1x) and Spreading Rate 3 (3x) PINTU

_ Logical Channels_ Radio Configurations_ Many new Physical Channels

_ Transmit Diversity Pilot Channels

_ Enhanced Access Channel

procedures

_ Reverse Link Pilot Channel

Spreading Rates

CDMA2000 supports two different spreading rates:

Spreading Rate 1 also called 1xBoth Forward and Reverse Channels use a single direct-sequence

spread carrier with a chip rate of 1.2288 Mcps.

Spreading Rate 3 also called 3x or MC (Multi-Carrier)

Forward Channels use three direct-sequence spread carriers each with a chip rate of

1.2288 Mcps.Reverse Channels use a single direct-sequence spread

carrier with a chip rate of 3.6864Mcps. As such SR3 appears to be

extinct.


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Physical and Logical Channels:

In IS 95A, in the forward link Pilot, Sync, Paging and Traffic Channels

exist where as in reverse link Access and traffic channel are

available. All overhead information is carried on the Paging Channel.During conversation or in dedicated mode the signaling info is

exchanged by either fully or partially clearing the traffic.

CDMA2000 technology defines new Physical and Logical Channels forthe transport of user data and signaling information.

A Physical Channel is a communication path between the mobile andthe Base Station, described in terms of the digital coding and RF

characteristics.A Logical Channel is a communication path within the protocol layersof either the Base Station or the mobile.

Radio Configurations: A Radio Configuration (RC) defines the following characteristics of a

Forward or Reverse Traffic Channel, Viz Rate Set, Spreading Rate Channel Coding

(Turbo or convolutional), Channel Coding Rate, Modulation (QPSK or BPSK)and TransmitDiversity Allowed.

IS-2000 defines Radio Configurations:

- RC1 and RC2 correspond to IS-95 A/B Rate Set 1 and Rate Set

2 respectively - RC3 through RC9 on the Forward link- RC3 through RC6 on the Reverse link

Variable Length Walsh Codes: Walsh Code used in IS95 is 64 chips long. CDMA20001x

can use Walsh Codes up to 128 Chips long. Higher data rate channels use shorter length

Walsh codes to

maintain a constant chip rate. Using one of the shorter Walsh codes precludes using alllonger codes that contain the bit pattern of the shorter code.

New Common Channels:

CDMA2000 introduces several new Forward Link Common Channels:

Pilot Channels - If transmit diversity is supported; one or more

Pilots may be used. The auxiliary Pilot Channels may be used for

smart antenna applications.

Quick Paging Channel - This channel provides for improved slotted mode

operation and improved battery life for the mobile. Walsh codes W80,W48 and W112 are reserved for Quick Paging Channels, if the Base

Station supports Quick Paging Channels.

Common Control Channel - This channel carries mobile-directed

messages for CDMA2000 compatible mobiles. Broadcast Channel - This channel carries broadcast messages for CDMA2000

compatible mobiles, including overhead messages and broadcast Short MessageService (SMS) messages.

Common Power Control Channel - This channel is used withEnhanced Access Channel Procedures (Reservation Mode), to send


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power control bits to the mobile so that Access Channel messages maybe sent under power control.

New Dedicated Channels:

CDMA2000 introduces several new Forward Link Dedicated Channels:

Forward Fundamental Channel - This channel is used for thetransmission of user and signaling information to a specific mobile during

a call. Each Forward Traffic Channel may contain one Forward

Fundamental Channel.

Forward Dedicated Control Channel - This channel is used fortransmission of user and signaling information to a specific mobileduring a call. Each Forward Traffic Channel may contain one ForwardDedicated Control Channel.

Forward Supplemental Channel (valid for Radio Configurations 3thro 9) This channel is used for the transmission of user informationto a specific mobile during a call. This is typically used for high-speed

data applications. Each Forward Traffic Channel may contain up to twoSupplemental Channels.

Power Control Subchannel - This subchannel is typicallyassociated with the Fundamental Channel, but if the F-FCH is notused for a given call, then it is associated with the Dedicated ControlChannel (F-DCCH).

All of the CDMA2000 dedicated channels can be established using

the TIA/EIA Paging (F-PCH) and Access (R-ACH) Channels.

Reverse Link Channels:

- Access Channel (R-ACH)

_ Reverse Pilot Channel (R-PICH)_ Enhanced Access Channel (R-EACH)

_ Reverse Common Control Channel (R-CCCH)_ Reversed Dedicated Control Channel (R-DCCH)

_ Reverse Fundamental Channel (R-FCH)_ Reverse Supplemental Channel (R-SCH)

_ Reverse Supplemental Code Channel (R-SCCH)

The Access Channel and Reverse Supplemental Channel are

retained for backward compatibility with TIA/EIA-95A/B. For Radio

Configurations 1 and 2, the channel structure for the Reverse

Fundamental Channel and Reverse Supplemental Channel is the sameas the channel structure of Rate Set 1 and Rate Set 2 used in TIA/EIA-

95A/B.

EV-DO


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EV-DO is a mobile technology that facilitates higher throughput on mobile platform.

The third generation of cellular standards has seen a dominance of CDMA as theunderlying access technology. UMTS (Universal Mobile Telecommunication Services)is 3G evolution for GSM world. The standardization work for UMTS is being carried-out

by 3GPP. The standardization work for CDMA 2000 and its enhancements is beingcarried out under the supervision of 3GPP2.

1x Evolution-Data Optimized, abbreviated as EV-DO or 1xEV-DO, is an evolution ofCDMA 2000 1x to support higher data rates. It is defined in TIA (TelecommunicationIndustry Association) standard IS 856. It is commonly referred to as DO. It is officiallytermed as "CDMA2000, High Rate Packet Data Air Interface". Working on same carrierbandwidth of 1.25 MHz as CDMA 2000 1x systems, 1xEV-DO provides significantlyhigher data rates to Access Terminals (mobile devices). Downlink data ratessupported are up to 2.4576 Mb/s in Rev. 0 and up to 3.1 Mb/s in Rev. A.

Traditional wireless networks create a physical path between receiving and sendingdevices, much like traditional telephone networks. EVDO instead adopts the sameapproach used for the internet. IP, the Internet Protocol, breaks data into small piecescalled packets. Each packet is sent independently of all the other packets. This savesbandwidth for use by other devices; when neither party on a phone call is speaking,the connection consumes no bandwidth because there are no packets to send. Radioresources are allocated only at the time of actual data transfer leading to betterspectral efficiency.

EV-DO does not support voice services. In Forward link supports data rates up to2.4576 Mbps. There is no power control in Forward Link. Peak data rate in ReverseLink is 153.6 kbps.

Generic Model of CDMA 2000 1x EVDO System:

A generic model of a CDMA 2000 1 x EV-DO System typically consists of:

a) Access Network (AN) consisting of Radio Node (RN) & Radio Network Controller

b) Packet Core Network (PCN)

a) Radio Node (RN): It is a multiple circuit transceiver which shall radiate to cover acell or a sector. It consists of radio modules, base band signal processor, networkinterface, antenna, feeder etc. It can be co-located with RNC or remotely located. RNshall include the functions related to channel coding/decoding, interleaving,encryption, frame building, modulation/demodulation, RF transceiver, antenna

diversity, low noise amplification etc. as per CDMA 2000 1 x EV-DO standards.

The AN obtains the timing reference and positioning reference from the GPSsystem and hence the GPS receiver shall form an integral part of the RN along withother fixtures such as GOS antenna, cable etc. AN split mounting arrangements withtower mountable RF components such as PAs, LNAs, Filters etc. are also acceptable.

b) Radio Network Controller (RNC): It is responsible for inter connection between theRN and the PCN and it provides control and management for one or more RNs. Itassigns traffic channels to individual users, monitors system performance and


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provides interface between the RN and the PCN. RNC performs the radio processingfunctions such as management of the radio resources, radio channel management,local connection management etc.

It also processes information required for decision on handover of calls fromone RN to another. RNC can be collocated with the PCN or remotely located.

The Packet Control Function (PCF) shall form an integral part of RNC.

Packet Core Network (PCN): The packet data core network provides packet dataservices to Access Terminal (AT) and consists of PDSN, HA, AAA, AN-AAA andFA functionalities. The functional entities AAA and ANAAA may be a single physicalentity or two separate physical entities.

Operations and Maintenance Centre (OMC): The Operations and Maintenance Centre(OMC) allow the centralized operation of the various units in the system and thefunctions needed to maintain the sub systems. The OMC provides the dynamicmonitoring and controlling of the network management functions for operation andmaintenance.

Call Processing in CDMA

Call processing refers to all the necessary functions that the system needs to carryout in order to set up, maintain, and tear down a call between a mobile and anotherparty.

Two types of connections are possible:

Mobile-to-Land call or Mobile-to-mobile call.

Call can be either mobile originated or mobile terminated. Since mobile station is thecommon element in both cases the IS-95 standard specifies the call states from theperspective of the CDMA.

States of mobile:

During normal operation, the mobile can occupy any one of the following states

Mobile station initialization state;

Mobile station idle state;

System access state;

Mobile station control on the traffic channel state.

After power-up, the mobile first enters the mobile station initialization state,where the mobile selects and acquires a system. Upon exiting the initialization

state, the mobile has fully acquired the system and its timing. Then the mobile enters the mobile station idle state where the mobile

monitors messages on the paging channel .

Any one of the following three events will cause the mobile to transition fromthe idle state to the system access state

1) The mobile receives a paging channel message requiring anacknowledgment or response,


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2) The mobile originates a call, or

3) The mobile performs a registration.

In the access state, the mobile sends messages to the base station on theaccess channel.

When the mobile is directed to a traffic channel, it enters the mobile stationcontrol on the traffic channel state where the mobile communicates with thebase station using the forward and reverse traffic channels. When the call isterminated, the mobile returns to the initialization state.

Initialization State

After power-up, the mobile enters the initialization state. This state contains four substates, which the mobile sequentially goes through:

1. System determination sub state;

2. Pilot channel acquisition sub state;

3. Sync channel acquisition sub state;

4. Timing change sub state

Idle State:

Paging Channel Monitoring

In the idle state, the mobile monitors the paging channel on the forward link. In orderto receive messages and receive an incoming call, the mobile needs to monitor thepaging channel for messages. The paging channel transmission is divided into slotsthat are 80 ms in length. There are two ways that the mobile can monitor the pagingchannel:

Nonslottedmode

Slotted mode.

In non-slotted mode, the mobile monitors the paging channel at all times. In slottedmode, the mobile monitors the paging channel only during assigned paging channelslots. Because the mobile doesnt have to monitor all the slots all the time, the mobileoperating in the slotted mode can conserve battery power.

Paging Channel Messages

There are a total of six overhead messages that are sent to the mobile on the pagingchannel:

System parameters message;

Neighbor list message; CDMA channel list message;

Extended system parameters message;

Global service redirection message;

Access parameter message.


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The first five messages are of configuration parameters and the last message is ofaccess information.

Access State

In the access state, the mobile transmits messages to the base station using theaccess channel. In addition, the mobile also receives messages from the base station

on the paging channel. There are six sub states that the mobile can occupy within theaccess state.

Update overhead information sub state;

Page response sub state;

Mobile station origination attempt sub state;

Registration access sub state;

Mobile station order/message response sub state;

Mobile station message transmission sub state.

Traffic channels state

The mobile may enter the traffic channel state from 2 sub states within the accessstate: the page response of state or the mobile state origination attempt sub state. Inother words after the mobile has successfully originated, the mobile may enter thetraffic channel state. In the traffic channel state, the mobile communicates with thebase station using the forward and reverse traffic channels. This state consists of 5sub states

traffic channel initialization sub state

waiting for order sub state

waiting for mobile state answer sub state

conversation sub state

release sub state

Hand Offs in CDMA

As the phone moves through a network the system controller transfers the call fromone cell to another, this process is called handoff. Handoffs maybe done with theassistance of the mobile or the system controller will control the process by itself.Handoffs are necessary to continue the call as the phone travels. Handoffs may alsooccur in idle state due to mobility.

Types of Handoffs in CDMA:There are primarily three types of Handoffs in CDMA.They are

Soft

Hard and

Idle.

The type of handoff depends on the handoff situation.


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To understand this we should know the cellular concept used in CDMA.

CDMA frequency- reuse planning (cellular concept):

Each BTS in a CDMA network can use all available frequencies. Adjacent cells cantransmit at the same frequency because users are separated by code channels, notfrequency channels. BTSs are separated by offsets in the short PN code This feature

of CDMA, called "frequency reuse of one," eliminates the need for frequency planning

Soft Handoff:

A soft handoff establishes a connection with the new BTS prior to breaking theconnection with the old one. This is possible because CDMA cells use the samefrequency and because the mobile uses a rake receiver. The CDMA mobile assists thenetwork in the handoff. The mobile detects a new pilot as it travels to the nextcoverage area. The new base station then establishes a connection with the mobile.

This new communication link is established while the mobile maintains the link withthe old BTS.

Soft handoffs are also called "make-before-break." Soft handoff can take place only

when the serving cell and target cell are working in the same frequency.


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TUTORIAL on CDMA Principles

1) MATCH THE FOLLOWING:

COLUMN-ACOLUMN-B

1)RF Spacing in CDMA:1)........

..A)Walsh code 0

2)RF Spacing in WCDMA2)........

..B) 869-889MHz

3) Pilot channel3)........

..C) Walsh code 32

4) Sync channel 4)..........

D) Walsh codes 1-7

5) Paging channel5)........

..E) 1.25 Mhz

6) Traffic channel6)........

..F) 824-844MHz

7) Reverse link freq

7)

. G) 1.25 Mhz

8) Forward link freq8)

I) Walsh codes 8-31, 33-63.

9)Space Diversity 9).. J)Employed by way of symbol interleaving

10)Time Diversity 10)K)Employed by way of multipath rake

receiver

2) SAY TRUE OR FALSE

1) CDMA is a spread spectrum technique.


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2) In CDMA all subs can use the same frequency.

3) Walsh codes are orthogonal codes to each other.

4) For soft hand off freq of operation of the cells involved should be same.

5) CDMA system uses FDD technique.

6) CDMA supports two rate sets for voice encoding.

7) In CDMA power control is applicable only for forward link.

8) Hard hand off is a break before make type.

9) No of access channels will be normally equal to no. of paging channels.

10) User mask is derived from electronic serial number of the hand set/ FWT.

11) Symbol is produced after coding process.

12) Chip is produced after spreading process.

13) CDMA system power control is applied only in the reverse link.

14) All CDMA system need GPS support for their functioning.

15) Long code is used for scrambling in the forward link.


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16) Short code gives the BTS ID.

3) CHOOSE THE BEST CORRECT ANSWER:

1) Softer hand off is of ____________ type A) break before make B) make

before break

2) Sequence used for spreading at trans end is 1001, then receiver will use ______

for despreading

A) 0110 B) 1001 C) 1010 D) 1111

3) Long code is of length A) 2^15-1 B) 2^42-1 C) 2^8-1

4) Long and short codes are: A) orthogonal codes B) pseudo random codes

C) none of the above

5) In forward link spreading is done by A) Walsh code B) Long code

6) If there are 4 shift registers in a PN code generator, the length of the code is

A) 15 bits B) 16 bits C) 8 bits

7) Forward link is A) BTS to mobile B) Mobile to BTS

8) Reverse link isA) BTS to mobile B) Mobile to BTS

9) Forward link works in A) 824- 849MHz B) 869-894MHz


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10) There are _____ no. of Walsh codes. A) 20 B) 64 C) 50

11) Length of each Walsh code is A) 64 chips B) 23 chips C) 12 chips

12)Space Diversity is achieved in cdma by

A) rake receiver B) Two antenna C) Booster antenna

Questions for CDMA2000-1X

1) MATCH THE FOLLOWING:

1) MSC-VLR 1)..........

A) E interface

2) MSC-HLR2).......

...B) 3G Standard

3) HLR-VLR3).......

...C) 3.6864Mcps

4) MSC-MSC

4).......

... D) N interface

5) HLR- SMC5).......

...E) peak data 2.4Mbps

6) CDMA IS 95 A network6).......

...F) C interface

7) CDMA 2000 1X-EVDO7).......

...

G) B interface

8) CDMA 20001X network8).......

...H) D interface

9) Spreading Rate 1 9) I)2G Standard


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10)Spreading Rate 310)

.J) 1.2288 Mcps.

2) SAY TRUE OR FALSE:

1) One BSC can control only one BTS

2) CC for India is 404

3) MCC for India is +91

4) MSIN and MIN are same.

5) ESN is a unique number assigned to the instrument.

6) CDMA IS 95A is a 2G standard.

7) IMT 2000 is the official name for 3G.

8) CDMA 2000 is backward compatible to IS 95A.

9) CDMA 2000 1x uses single carrier.

10) CDMA 2000 3x is multi carrier system.

11) RC1 and2 of CDMA2000 correspond to rate set 1 and2 of IS95A.

12) Variable length Walsh Codes are used in IS95A


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13) In RC1 and RC2 the no. of supplemental channels are seven maximum.

cdma handout for summer trg

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