Introduction to CDMA2k

NI-RFmx Waveform Creator User Guide 2.4

Edition Date: November 2017

Part Number: 377063C-01

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CDMA2k is a standard for 3G wireless technology that is derived from cdmaOne (IS95). Signals are specified by radio configurations. Two chip rates are supported on the reverse link; 1.2288 Mchips/sec (spreading rate 1) and 3.6864 Mchips/sec (spreading rate 3). Currently only spreading rate 1 is supported on the downlink.

CDMA2k Reverse (Uplink) Channels

  1. Access Channel (ACH)

    This is a slotted random access channel that is used for short signaling message exchanges with the base station. For example, call origination.


  2. Reverse traffic channel

    The reverse traffic channel is composed of up to one reverse dedicated control channel (DCCH) (radio configurations 3 to 4), up to one reverse fundamental channel (FCH), zero to two reverse supplemental channels (SCH) (only for radio configurations 3 and 4) and zero to seven reverse supplemental code channels (SCCH) (only for radio configurations 1 and 2). Note that NI-RFmx Waveform Creator does not currently support reverse supplemental code channels.


  3. Enhanced access channel (EACH)

    The enhanced channel is used for transmission of short messages, such as signaling, response to pages and call origination. It can also be used to transmit moderately sized data packets (only for radio configurations 3 and 4).


  4. Reverse common control channel (CCCH)

    This is the portion of the reverse channel that is used for the transmission of digital control information from one or more mobile stations to a base station. This is only available in radio configurations 3 and 4.


  5. Reverse pilot channel (PICH)

    This is an unmodulated, direct spread spectrum signal transmitted continuously by a mobile station. The reverse pilot channel provides a phase reference for coherent demodulation as well as a means for signal strength measurement. Note that the pilot channel is part of the reverse common control channel and the enhanced access channel. Only present in radio configurations 3 and 4.


Reverse (Uplink) Channels at Spreading Rate 1

There are four radio configurations for the reverse traffic channel at spreading rate 1. For completeness, these are given in the following table. These radio configurations define the allowed data rates and the modulation scheme.



Table 4-1 Radio configurations for the reverse channel


The Channel types supported by NI-RFmx Waveform Creator and that are allowed at spreading rate 1 are given in the following table.



Table 4-2 Channel types per mobile station on the reverse CDMA channel for spreading rate 1


The structures for the various reverse channels are given in the following tables. Refer to Appendix B for further information regarding symbol rate and data rate for each of the channels.



Fig. 4-1 Channel structure for the access channel for spreading rate 1


Note that NI-RFmx Waveform Creator does not currently implement the blocks contained within grayed regions shown in the following figure.



Fig. 4-2 Channel structure for the reverse fundamental channel and reverse supplemental code channels (radio configurations 1 and 2)


The long code generators use a user mask (Long code mask) to define the output sequence. A combination of short and long codes is used to scramble the data in radio configurations 3 and 4 as shown in the following figure.



Fig. 4-3 I and Q mapping for the reverse pilot channel, enhanced access channel, reverse common control channel and the reverse traffic channel with radio configuration 3 and 4


Reverse (Uplink) Channels at Spreading Rate 3

For spreading rate 3, only radio configurations 5 and 6 are allowed. This implies that the allowed channel types are as given in the following figure.



Table 4-3 Channel types on the reverse channel for spreading rate 3


The I and Q mapping for the higher spreading rate is given in the following figure. Note that in essence this is identical to that given in the above figure. In general, the higher data rates are achieved by repeating the Walsh spreading three times for each input symbol. Note also that the long code generates data at 3.6864 Mcps as opposed to 1.2288 Mcps.



Fig. 4-4 I and Q mapping for spreading rate 3


CDMA2k Forward (Downlink) Channels

The forward transmission of CDMA2k consists of several channels. These are:

  1. Auxiliary pilot channel (APICH)

    An unmodulated, direct sequence spread spectrum signal transmitted continuously by each CDMA base station. An auxiliary pilot channel is required for forward link spot beam and antenna beam forming applications, and provides a phase reference for coherent demodulation of those forward CDMA channels associated with the auxiliary pilot.


  2. Auxiliary transmit diversity pilot channel (ATDPICH)

    A transmit diversity pilot channel associated with an auxiliary pilot channel. These two pilot channels are used to assist with coherent demodulation when channels that employ transmit diversity are used. Transmit diversity is not supported by NI-RFmx Waveform Creator.


  3. Broadcast channel (BCCH)

    A code channel in a forward CDMA channel used for the transmission of control information and pages from a base station to a mobile station. The BCCH is used to send control information to mobile stations that have not been assigned to a Traffic Channel.


  4. Common assignment channel (CACH)

    A forward common channel used by the base station to acknowledge a mobile station accessing the enhanced access channel.


  5. Common power control channel (CPCCH)

    A forward common channel that transmits power control bits to multiple mobile stations.


  6. Forward common control channel (CCCH)

    A control channel used for the transmission of digital control information from a base station to one or more mobile stations.


  7. Forward dedicated control channel (DCCH)

    A portion of the radio configuration 3 to 9 forward traffic channel that is used for the higher level data, control information and power control information from a base station to a mobile station.

  8. Forward fundamental channel (FCH)

    A portion of the forward traffic channel that carries a combination of higher-level data and power control information. It carries user data, such as voice, signaling and low rate data.


  9. Forward pilot channel (PICH)

    An unmodulated, direct sequence spread spectrum signal transmitted continuously by each CDMA base station. The PICH allows a mobile to acquire the timing of the forward CDMA channel.


  10. Forward supplemental channel (SCH)

    A portion of a radio configuration 3 to 9 forward traffic channel which operates in conjunction with a forward fundamental channel or a forward dedicated control channel to provide higher data rates.


  11. Forward supplemental code channel (SCCH)

    A portion of a radio configuration 1 and 2 forward traffic channel which operates in conjunction with a forward fundamental channel and (optionally) with other forward supplemental code channels to provide higher data rates.


  12. Paging channel (PCH)

    A code channel in a forward CDMA channel used for the transmission of control information and pages from a base station to a mobile station.


  13. Quick paging channel (QPCH)

    An uncoded, spread and on-off-keying modulated spread spectrum sent by a base station to inform mobile stations operating in the slotted mode during the idle state whether to receive the forward common control channel or the paging channel starting in the next forward common control channel or paging channel frame.


  14. Sync channel (SYNCH)

    A code channel in the forward CDMA channel that transmits the synchronization message to the mobile station.


  15. Transmit diversity pilot channel (TDPICH)

    An unmodulated, direct spread spectrum signal transmitted continuously by a CDMA base station to support forward link transmit diversity. NI-RFmx Waveform Creator does not support transmit diversity.


CDMA2k Forward Channels (Downlink) at Spreading Rate 1

There are five radio configurations for the forward traffic channel at spreading rate 1. These are given in the following table. The radio configurations define the types of channel allowed as well as allowed data rates.



Table 4-4 Radio configurations for the forward channel at spreading rate 1


The channel types supported by NI-RFmx Waveform Creator and that that are allowed at spreading rate 1 are given in the following table.



Table 4-5 Channel types on the forward link for spreading rate 1


The structures for these forward channels are given in Fig. 4-5 through to Fig. 4-6. NI-RFmx Waveform Creator does not currently implement blocks within the gray areas shown in these figures.



Fig. 4-5 Pilot channels, sync channel and paging channels for spreading rate 1




Fig. 4-6 Structure for the broadcast, common assignment and forward common control channels for spreading rate 1


Note: In NI-RFmx Waveform Creator the common assignment channel always has a message present.



Fig. 4-7 Quick paging channel structure for spreading rate 1




Fig. 4-8




Fig. 4-9 Forward traffic channel structure for the forward traffic channel with radio configurations 3, 4, and 5




Fig. 4-10 Demultiplexer structure for spreading rate 1


The DEMUX functions distribute input symbols sequentially from the top to the bottom of the output paths. The outputs are fed in the following figure.



Fig. 4-11 I and Q mapping (Non-OTD Mode) for spreading rate 1


In the above figure the inputs are spread with a Walsh function that may also be modified by a quasi-orthogonal function termed a QOF. This in turn can be modified further by rotating the complex vector 90 degrees. A Walshrot value of 0 implies no rotation. A value of 1 implies rotate by 90 degrees. All channels are scrambled using a complex scrambling code. Note that radio configurations 1 and 2 use the null QOF: in other words, the Walsh functions are not altered.

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