EVDO Rel A Basic-20081212

EVDO Basics

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Contents

CDMA Evolution Path Comparison between CDMA 1X and EVDO Forward Link Frame Structure Reverse Link Frame Structure Forward Link Channel Structure Reverse Link Channel Structure


CDMA Evolution Path


Comparison between CDMA 1X and EVDO1X 1X EVDO Rev 0 1X EVDO Rev A

Data Type Data + Voice Data Data + VoIP

Max Data Rate (Forward Link)

307.2 Kbps 38.4 kbps-2.45676 Mbps

3.1 Mbps

Max Data Rate (Reverse Link)

307.2 Kbps 9.6 kbps - 153.6 kbps 4.8 kbps -1.8 Mbps

Forward Link Channels for Packet Data

F-FCH, F-SCH, F-SCCH

Traffic/Pilot/MACMAC= RPC,RA,DRC Lock

Traffic/Pilot/MACMAC= RPC,RA,DRC Lock, ARQ

Reverse Link Channels for Packet Data

R-FCHR-SCH

Pilot/ACK/Data/MAC=RRI, DRC

Pilot/ACK/Data/MAC=RRI,DRC,DSC

Data Control Power Channel

Power Control Sub Channels (RL/FL)

-RRI-RPC (Fwd MAC Ch)

-RRI-RPC (Fwd MAC Ch)

Modulation BPSK, QPSK QPSK,8-PSK, QAM QPSK,8-PSK, QAM

Channel Coding Convolution /Turbo Turbo Turbo

FL Data Rate selection

Base Station MS MS

FL Power Management

Variable Full Power Full Power


Forward Link Frame Structure On the fwd link, EV-DO Rev 0 uses TDMA in tandem with CDMA. 1 CDMA channel is 32768 chips long and lasts 26.67ms. This is one

physical channel comprising of time multiplexed channels – Pilot, MAC, Traffic & Control.

The FL is broken up into slots. Each slot is of duration 1.667ms. A set of 16 slots make up a group called a “frame” (duration: 26.67ms).

Some slots are used to carry the control channel for everyone to hear; most slots are intended for individual users.

Each slot is transmitted at maximum power. Users don’t “own” long continuing series of slots like in TDMA or GSM;

instead, each slot or small string of slots is dynamically addressed to whoever needs it at the moment.


Forward Slot Structure

The main “cargo” in a slot is the DATA being sent to a user But all users need to get continuous timing and administrative information,

even when all the slots are going to somebody else. Twice in every slot there is regularly-scheduled burst of timing and

administrative information for everyone to use • MAC (Media Access Control) information such as power control bits • a burst of pure Pilot – allows new mobiles to acquire the cell and decide to use it – keeps existing user mobiles exactly on sector time – mobiles use it to decide which sector should send them their next forward

link packet In case there are no ATs having active connections with an Access Node (AN) or

Base Station (BTS), the AN still transmits the pilots. In such a scenario, each pilot burst is guarded by two 64 chip “guard”/”skirt” bursts which improves pilot acquisition and SNR computation by the ATs



Control Channel Cycle

A Control Channel Cycle is 16 frames ( 16*26.67ms = 436.67 ms) The first half of the first frame has all of its slots reserved for

possible use carrying Control Channel packets The last half of the first frame, and all of the remaining 15

frames, have their slots available for ordinary use transmitting sub packets to users


Reverse Link Frame Structure


1 X EVDO Channel Overview

AN AT

• Pilot Channel•Forward Control Channel• Forward Traffic Channel•MAC = Rev Activity (RA), Rev Power Control (RPC), DRC Lock, ARQ

• Pilot Channel• Data Channel

• Pilot Channel• Aux Pilot• MAC = Rev Rate Indicator(RRI), Data Rate Control

(DRC), Data Source Control (DSC)• ACK (Acknowledgement ) Channel• Data Channel

Forward Channel (TD-CDMA)

Reverse Access Channel

Reverse Traffic Channel


Forward Channel Structure

Forward

Pilot Control TrafficMedium

Access Control (MAC)

Reverse Activity DRC Lock Reverse Power

Control ARQ


Forward Channel StructureThe 1X EVDO forward channel structure is time multiplexed in the following Channels: The pilot channel comprises of a simple sequence of zeros, covered by the reserved Walsh cover 64W0. Pilot Channel used by AT for:

Initial Acquisition Phase and Timing recovery Coherent demodulation Estimate receive C/I for forward data rate control

The MAC channel contains information for the set of active ATs in the sector. It also acts as a “guard” for the pilot burst in each slot.MAC consists of two sub channels:

Reverse Activity Channel : The Reverse Activity (RA) Channel transmits the Reverse Activity Bit (RAB) stream over the MAC Channel with MACIndex 4. The RA bit is transmitted in every slot at an effective data rate of 600 bps. The AT uses this information to help determine the data rate for transmission on the reverse link. Reverse Power Control: In Rel A, RPC updates are sent at a rate of 150 bps (updates/second). In Rel 0, RPC is done at 600 bps. ‘0’ means increase AT power and ‘1’ means decrease AT power. The DRC Lock sub-channel indicates to the AT whether the DRC information sent by the AT was correctly decoded at the AN or not.The ARQ channel coupled with the Data Rate Control (DRC) and Ack Channel provides the handshake to increase the Access Terminal’s data throughput performance, resulting in increased capacity of the system.


The RPC, ARQ and DRC Lock channels are multiplexed together as per the following table.

The RPC Channel is time-division multiplexed with the ARQ Channel and transmitted in 1 slot out of every 4 slots.


Control channel combines the functions of the synchronization, paging and system information channels. This channel is time division multiplexed with the traffic channel, on the data portion of the slot. A control channel packet is transmitted at least once every 256 slots (or 16 frames). The CCH is transmitted either at 38.4 or at 76.8 Kbps.

The traffic channel carries the user data. This stream is time division multiplexed with the control channel, on the data part of each slot.

The Forward Traffic Channel carries user data in the form of encoded Physical Layer packets. Transmission is a variable rate from 38.4 kbps up to 2.4576 Mbps. The number of slots used is a function of the data rate.

The transmission of the Pilot and MAC Channels is synchronized between all sectors within a network. This permits the AT to measure all pilots simultaneously.

Transmissions from all sectors are synchronized, yielding overlapped pilot burst at the AT receiver. This is the basis for estimating the co-channel interference. In the case of the transmission of Idle slots, the adjacent MAC channels provide overlap margin against differential over the air time delay skew.


MAC Index The RPC and DRC Lock sub-channels are time division multiplexed on

the MAC channel. The RAC is code division multiplexed with the RPC/DRC Lock.

The AN must “address” the RPC/DRC Lock sub-channels for the intended AT. The addressing is achieved using a “MAC Index” that is assigned to each active AT in the sector


Reverse Channel Structure

Indicates that the channel is newly introduced in Rel A


The access channel is used by the AT to initiate communication with the AN or to respond to a page.

Each access probe consists of a preamble followed by an access channel data packet. The preamble duration is 1 frame, or 16 slots. During the preamble, only the pilot channel is transmitted. The access channel data packet is transmitted over 4 frames. During the access channel data packet, both the pilot and access data packets are transmitted using code division multiplexing.

The pilot channel is transmitted over the I-phase and the Data Channel is transmitted over the Q-Phase.

Access Channel


The RL traffic channel consists of code division multiplexed information streams on I and Q phases.

CDM (Code Division Multiplexing) is utilized to simultaneously transmit multiple channels.

The ACK and DSC channel are time-multiplexed together. The auxiliary pilot channel is optional and is used at higher rates. The pilot channel in the reverse traffic channel structure is different from

that in the access channel structure.

Traffic Channel


The reverse link Pilot Channel transmits a string of unmodulated symbols with a binary value of 0 using a 16-bit Walsh Code 0 over the In-phase channel.

Reverse Link Traffic Auxiliary Pilot Channel is transmitted in addition to the regular pilot channel. at high data rates, the process of demodulation can be enhanced by allowing transmission of an auxiliary pilot channel. the auxiliary pilot is transmitted only when the payload meets or exceeds a configurable threshold. This threshold ranges between 128 and 12288 bits.

The auxiliary pilot consists of all 0s spread with the 32-bit Walsh Code 28.

The power level of the auxiliary pilot is specified relative to the pilot channel.

The Reverse Link MAC channel consists of the following channels separated by a Walsh Code:

Reverse Rate Indicator (RRI) channel Data Rate Control (DRC) channel Data Source Control (DSC) channel


Reverse Rate Indication (RRI) ChannelRRI Channel is transmitted using it’s own 16-chip Walsh Code over the In-Phase

channel.The RRI channel is a 6 bit symbol that – 4 bits to indicate the payload size and 2 bit sub-

packet identifier. The sub-packet identifier of the current transmission facilitates reverse link H-ARQ and

the payload size identification assists in avoiding blind rate detection at the AN. Data Rate Control Channel (DRC)The DRC channel is used by the AT to indicate the serving sector as well as the

requested data rate.A 4 bit DRC value specifies the data rate and the serving sector is identified via 8-ary

Walsh code function. The Walsh code also performs the function of spreading the DRC channel.

DRC 13 corresponds to a nominal data rate of 1.536 Mbps, and DRC 14 allows the Forward Traffic Channel transmission to be as high as 3.072 Mbps.

Data Source Control Channel (DSC)The purpose of the DSC is to give the RNC advance notice of the AT’s intent to switch

cells. Therefore, while the RNC is transitioning the data to the new cell, the AT can continue requesting data from its current cell. The use of the DSC reduces the inter-cell latency.

The DSC channel is time-division multiplexed with the ACK channel and is always transmitted in the second half slot.


The DSC value is effective one slot after its transmission and stays in effect for a duration specified by the DSCLength.

The DSC values are transmitted at a rate of 600/DSCLength per second.

The ACK channel is time-division multiplexed with the DSC channel and is always transmitted in the first half slot. It is used by the AT to confirm the successful reception of a packet or indicate that a packet was not received.

The Reverse Link Traffic Data Channel carries the user data. The Reverse Traffic Channel utilizes sub-frames to transmit sub-packets (1 sub-packet = 4 slots = 6.67ms). The data rate can change every 6.67ms.


All the reverse channels are orthogonally spread with Walsh functions called Walsh covers at a chip rate of 1.2288 Mcps.

Pilot Channel : 16-chip Walsh function number 0 --

Ack Channel : 8-chip Walsh function number 4 --

DRC Channel : 16-chip Walsh function number 8 –

Data Channel : 4-chip Walsh function number 2 –

Each traffic is direct sequence spread by a distinct user PN code sequence.

160W84W168W42W

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EVDO Rel A Basic-20081212