CDMA Technology OverviewFebruary, Page 1-1 CDMA Technology Overview Lesson 1 – CDMA Basics

CDMA Technology OverviewFebruary, Page 1-2 Course Objectives Upon completion of this course, you will have an understanding of the following concepts: CDMA and other access technologies CDMA coding, forward, and reverse channels Vocoding, multiplexing, and power control Components that comprise a CDMA system CDMA messaging and call flow

CDMA Technology OverviewFebruary, Page 1-3 Why CDMA? CDMA is the technology of choice for both 800 MHz Cellular and 1900 MHz PCS service providers CDMA satisfies CTIA Users’ Performance Requirements CDMA provides high capacity (many times the capacity of AMPS) CDMA provides privacy through its coding scheme CDMACDMA CDMACDMA ode ivision ultiple ccess CDMA is extremely robust and provides excellent audio quality

CDMA Technology OverviewFebruary, Page 1-4 What is Multiple Access? Since the beginning of telephony and radio, system operators have tried to squeeze the maximum amount of traffic over each circuit Types of Media  Twisted pair - copper  Coaxial cable  Fiber optic cable  Air interface (radio signals) Advantages of Multiple Access  Increased capacity: serve more users  Reduced capital requirements since fewer media can carry the traffic  Decreased per-user expense  Easier to manage and administer Each pair of users enjoys a dedicated, private circuit through the transmission medium, unaware that the other users exist. Multiple Access: Simultaneous private use of a transmission medium by multiple, independent users.

CDMA Technology OverviewFebruary, Page 1-5 Multiple Access Technologies The physical transmission medium is a resource that can be subdivided into individual channels according to different criteria depending on the technology used: Here’s how the three most popular technologies establish channels:  FDMA (Frequency Division Multiplex Access)  each user on a different frequency  a channel is a frequency  TDMA (Time Division Multiplex Access)  each user on a different window period in time (“time slot”)  a channel is a specific time slot on a specific frequency  CDMA (Code Division Multiplex Access)  each user uses the same frequency all the time, but mixed with different distinguishing code patterns  a channel is a unique set of code patterns Frequency Time Power Frequency Time Power Frequency Time Power FDMA TDMA CDMA Channel :An individually-assigned, dedicated pathway through a transmission medium for one user’s information

CDMA Technology OverviewFebruary, Page 1-6 CDMA System Components Mobile Telephone Exchange (MTX) provides call processing functions for AMPS/TDMA/CDPD/CDMA cellular systems Base Station Manager (BSM) provides a Graphical User Interface (GUI) for operations, administration and maintenance of the BSC, BTS and itself Base Station Controller (BSC) provides data routing, voice coding and some hand-off functions Base Station Transceiver Subsystem (BTS) provides the RF link to the subscriber MTX, BSC and BSM are identical for 800 and 1900 MHz products Mobile Telephone Exchange (MTX) provides call processing functions for AMPS/TDMA/CDPD/CDMA cellular systems Base Station Manager (BSM) provides a Graphical User Interface (GUI) for operations, administration and maintenance of the BSC, BTS and itself Base Station Controller (BSC) provides data routing, voice coding and some hand-off functions Base Station Transceiver Subsystem (BTS) provides the RF link to the subscriber MTX, BSC and BSM are identical for 800 and 1900 MHz products DMS-MTX BTS T1 or E1s MTSO T1s BSM BSC MAP

CDMA Technology OverviewFebruary, Page 1-7 Defining Our Terms nCDMA Channel or CDMA Carrier or CDMA Frequency  Duplex channel made of two 1.25 MHz-wide bands of electromagnetic spectrum, one for Base Station to Mobile Station communication (called the FORWARD LINK or the DOWNLINK) and another for Mobile Station to Base Station communication (called the REVERSE LINK or the UPLINK)  In 800 Cellular these two simplex 1.25 MHz bands are 45 MHz apart  In 1900 MHz PCS they are 80 MHz apart nCDMA Forward Channel  1.25 MHz Forward Link nCDMA Reverse Channel  1.25 MHz Reverse Link nCDMA Code Channel  Each individual stream of 0’s and 1’s contained in either the CDMA Forward Channel or in the CDMA Reverse Channel  Code Channels are characterized (made unique) by mathematical codes  Code channels in the forward link: Pilot, Sync, Paging and Forward Traffic channels  Code channels in the reverse link: Access and Reverse Traffic channels 45 or 80 MHz CDMA CHANNEL CDMA Reverse Channel 1.25 MHz CDMA Forward Channel 1.25 MHz

CDMA Technology OverviewFebruary, Page 1-8 CDMA Is a Spread-Spectrum System  Traditional technologies try to squeeze the signal into the minimum required bandwidth  Direct-Sequence Spread spectrum systems mix their input data with a fast spreading sequence and transmit a wideband signal  The spreading sequence is independently regenerated at the receiver and mixed with the incoming wideband signal to recover the original data  The de-spreading gives substantial gain proportional to the bandwidth of the spreading signal  CDMA uses a larger bandwidth but then uses resulting processing gain to increase capacity Spread Spectrum Payoff: Processing Gain Spread Spectrum TRADITIONAL COMMUNICATIONS SYSTEM Slow Information Sent TX Slow Information Recovered RX Narrowband Signal SPREAD-SPECTRUM SYSTEM Fast Spreading Sequence Slow Information Sent TX Slow Information Recovered RX Fast Spreading Sequence Wideband Signal

CDMA Technology OverviewFebruary, Page 1-9 Spread Spectrum Principles 1.25 MHz 30 KHz Power is “Spread” Over a Larger Bandwidth MATH HAMMER MATH HAMMER

CDMA Technology OverviewFebruary, Page 1-10 Spread Spectrum Principles Many code channels are individually “spread” and then added together to create a “composite signal”

CDMA Technology OverviewFebruary, Page 1-11 Spread Spectrum Principles UNWANTED POWER FROM OTHER SOURCES Using the “right” mathematical sequences any Code Channel can be extracted from the received composite signal

CDMA Technology OverviewFebruary, Page 1-12 Anything We Can Do, We Can Undo nAny data bit stream can be combined with a spreading sequence nThe resulting signal can be de-spread and the data stream recovered if the original spreading sequence is available and properly synchronized nAfter de-spreading, the original data stream is recovered intact ORIGINATING SITEDESTINATION Spreading Sequence Spreading Sequence Input Data (Base Band) Recovered Data (Base Band) Spread Data Stream (Base Band + Spreading Sequence)

CDMA Technology OverviewFebruary, Page 1-13 “Shipping and Receiving” via CDMA nWhether in shipping and receiving, or in CDMA, packaging is extremely important! nCargo is placed inside “nested” containers for protection and to allow addressing nThe shipper packs in a certain order, and the receiver unpacks in the reverse order nCDMA “containers” are spreading codes FedEx Data Mailer FedEx Data Mailer ShippingReceiving

CDMA Technology OverviewFebruary, Page 1-14 CDMA’s Nested Spreading Sequences nCDMA combines three different spreading sequences to create unique, robust channels nThe sequences are easy to generate on both sending and receiving ends of each link nThe sequences are applied in succession at the sending end and then reapplied in opposite order to recover the original data stream at the receiving end Spreading Sequence A Spreading Sequence B Spreading Sequence C Spreading Sequence C Spreading Sequence B Spreading Sequence A Input Data X Recovered Data X X+AX+A+BX+A+B+CX+A+BX+A Spread-Spectrum Chip Streams ORIGINATING SITEDESTINATION

CDMA Technology OverviewFebruary, Page 1-15 Walsh Codes 64 Sequences, each 64 chips long a chip is a binary digit (0 or 1) Each Walsh Code is Orthogonal to all other Walsh Codes It is possible to recognize, and therefore extract, a particular Walsh code from a mixture of other Walsh codes that are “filtered out” in the process Two same-length binary strings are orthogonal if the result of XORing them has the same number of 0s as 1s WALSH CODES # Chip Sequence EXAMPLE: Correlation of Walsh Code #23 with Walsh Code #59 # # XOR Correlation Results: 32 1’s, 32 0’s: Orthogonal!!

CDMA Technology OverviewFebruary, Page 1-16 Correlation and Orthogonality Correlation is a measure of the similarity between two binary strings Code # –(Code #23) Code # PARALLEL XOR: all 0s Correlation: 100% (100% match) Correlation: 100% (100% match) ORTHOGONAL XOR: half 0s, half 1s Correlation: 0% (50% match, 50% no-match) Correlation: 0% (50% match, 50% no-match) ANTI-PARALLEL XOR: all 1s Correlation: –100% (100% no-match) Correlation: –100% (100% no-match) #23 –(#23) #23 #59

CDMA Technology OverviewFebruary, Page 1-17 Creating the Walsh Code Table 00 01

CDMA Technology OverviewFebruary, Page 1-18 Creating the Walsh Code Table

CDMA Technology OverviewFebruary, Page 1-19 Creating the Walsh Code Table

CDMA Technology OverviewFebruary, Page Creating the Walsh Code Table

CDMA Technology OverviewFebruary, Page 1-21 Creating the Walsh Code Table

CDMA Technology OverviewFebruary, Page 1-22 The Short PN Sequences The two Short PN Sequences, I and Q, are 32,768 chips long Together they can be considered a two-dimensional binary “vector” with distinct I and Q component sequences, each 32,768 chips long Each Short PN Sequence (and, as a matter of fact, any sequence) correlates with itself perfectly if compared at a timing offset of 0 chips Each Short PN Sequence is special: Orthogonal to a copy of itself that has been offset by any number of chips (other than 0) I Q 32,768 chips long 26 2 / 3 ms. (75 repetitions in 2 sec.) I Q I Q 100% Correlation: All bits = 0 Short PN Sequence vs. 0 Offset I Q I Q Orthogonal: 16,384 1’s + 16,384 0’s Short PN Sequence vs. Any Offset Unique Properties:

CDMA Technology OverviewFebruary, Page 1-23 The Long PN Sequence Each mobile station uses a unique User Long Code Sequence generated by applying a mask, based on its 32-bit ESN, to the 42-bit Long Code Generator which was synchronized with the CDMA system during the mobile station initialization Generated at Mcps, this sequence requires 41 days, 10 hours, 12 minutes and 19.4 seconds to complete Portions of the Users Long Codes generated by different mobile stations for the duration of a call are not exactly orthogonal but are sufficiently different to permit reliable decoding on the reverse link Long Code Register MCPS) Public Long Code Mask (STATIC) User Long Code Sequence MCPS)

CDMA Technology OverviewFebruary, Page 1-24 How Many Spreading Codes Do We Need? ( Discriminating Among Forward Code Channels) nA Mobile Station tuned to a particular CDMA frequency receives a Forward CDMA Channel from a sector in a Base Station. nThis Forward CDMA Channel carries a composite signal made of up to 64 forward code channels nSome of these code channels are traffic channels while other are overhead channels needed by the CDMA system to operate properly. nA set of 64 mathematical codes is needed to differentiate the 64 possible forward code channels that can be contained in a Forward CDMA Channel. The codes in this set are called “Walsh Codes” Sync Pilot FW Traffic (for user #1) Paging FW Traffic (for user #2) FW Traffic (for user #3)

CDMA Technology OverviewFebruary, Page 1-25 How Many Spreading Codes Do We Need? ( Discriminating Among Base Stations) nA mobile Station is surrounded by Base Stations, all of them transmitting on the same CDMA Frequency nEach Sector in each Base Station is transmitting a CDMA Forward Traffic Channel containing up to 64 distinct forward code channels nA Mobile Station must be able to discriminate between different Sectors of different Base Stations and listen to only one set of code channels nTwo binary digit sequences called the I and Q Short PN Sequences (or Short PN Codes) are defined for the purpose of identifying sectors of different base stations nThese Short PN Sequences can be used in 512 different ways in a CDMA system. Each one of them constitutes a mathematical code which can be used to identify a particular sector of a particular base station AB Up to 64 Code Channels Up to 64 Code Channels

CDMA Technology OverviewFebruary, Page 1-26 How Many Spreading Codes Do We Need? ( Discriminating Among Reverse Code Channels) nThe CDMA system must be able to uniquely identify each Mobile Station that may attempt to communicate with a Base Station nA very large number of Mobile Stations will be in the market nOne binary digit sequence called the Long PN Sequence (or Long PN Code) is defined for the purpose of uniquely identifying each possible reverse code channel nThis sequence is extremely long and can be used in trillions of different ways. Each one of them constitutes a mathematical code which can be used to identify a particular user (and is then called a User Long Code) or a particular access channel (explained later in this course) RV Traffic from M.S. # RV Traffic from M.S. # RV Traffic from M.S. # System Access Attempt by M.S. # (on access channel #1)

CDMA Technology OverviewFebruary, Page 1-27 Summary of Characteristics & Functions Cell Each CDMA spreading sequence is used for a specific purpose on the forward link and a different purpose on the reverse link The sequences are used to form “code channels” for users in both directions Walsh Codes Short PN Sequences Long PN Sequences Type of Sequence Mutually Orthogonal Orthogonal with itself at any time shift value except 0 near- orthogonal if shifted Special Properties How Many 64 chips 1/19,200 sec. 32,768 chips 26-2/3 ms 75x in 2 sec chips ~41 days Length Orthogonal Modulation (information carrier) Quadrature Spreading (Zero offset) Distinguish users Reverse Link Function User identity within cell’s signal Distinguish Cells & Sectors Data Scrambling to avoid all 1’s or 0’s Forward Link Function I Q 32,768 chips long 26-2/3 ms. (75 repetitions in 2 sec.) 64 codes 64 chips long AND = SUM Modulo-2 Addition

CDMA Technology OverviewFebruary, Page 1-28 Lesson Review 1.If a signal is deliberately transmitted using more RF bandwidth than required, it is easier to detect at the receiver. This “waste” is formally defined as what? Processing gain 2.What vocoder function stores a collection of arbitrary waveform segments? Code book 3.Are all CDMA Walsh Codes orthogonal? Yes 4.What sequence best describes this conversion relationship in CDMA: chips  symbols  bits 5.List the four overhead (support) channels. Paging, sync, access, pilot

CDMA Technology OverviewFebruary, Page 1-29