There is several new CDMA2000 channels that are used within the CDMA2000 1X system. CDMA2000 builds on IS-95 cdmaOne, and as a result it utilises many of the channels that were found on the original system. However to provide the additional functionality and performance a number of new CDMA2000 channels have been incorporated.
As with IS-95, the CDMA2000 channels are different between the forward and reverse links.
CDMA2000 channels in the forward link
The new CDMA2000 channels used iont he system are outlined below.
- Forward pilot channel (F-PICH : This CDMA2000 channel is the same as it was on IS-95. It carries no data, and uses Walsh Code 0. As the Walsh code 0 is used, this is all zeros and therefore its length is immaterial and it therefore retains compatibility with IS-95.
- Forward Transmit Diversity Pilot Channel (F-TDPICH): While the F-PICH channel remains the primary pilot channel, this CDMA2000 channel is used to provide a pilot for transmit diversity when two antennas are used. It provides a timing reference for the second antenna diversity signals. As F-PICH is the primary channel, this one is normally set at a power level below it.
- Forward Dedicated Auxiliary Pilot Channel (F-APICH): This channel is used when smart antennas are used. Under these circumstances a sector can be further divided into smaller sector beams and this can be used to reduce the levels of interference. When this is implemented, each of these beams forms a new sector and needs its own pilot channel.
- Forward Auxiliary Transmit Diversity Pilot Channel (F-ATDPICH): This CDMA2000 channel is required when transmitting diversity in each beam when using a smart antenna system.
- Forward Sync Channel (F-SYNCH): This channel provides the same functionality and operates in the same fashion as for IS-95. The timing of this CDMA2000 channel is also aligned with that of the pilot channel and as a result the mobile is able to easily decode the sync channel messages. Some additional information does need to be transmitted on this channel. For example it is necessary to inform the mobile whether the base station is 1X or 3X compatible.
- Forward Paging Channel (F-PCH): This paging channel retains the same structure as that used for IS-95, but a number of enhancements have been introduced for CDMA2000.
- Forward Quick Paging Channel (F-QPCH): This channel provides information to the mobile so that it can use slotted reception for its sleep mode. For IS-95 the mobile awoke at specific times to check the paging channel which also carried other information. The Forward Quick Paging Channel is dedicated to this function and is able to perform it more effectively. Using the Paging Channel in IS-95 the receiver had to wake up and receive a 96 mS slot, whereas using the F-QPCH it only needs to wake up and receive a 5 mS slot. This gives a significant reduction in the time the receiver needs to be awake, and considerably extends the standby battery life.
- Forward Common Control Channel (F-CCCH): The F-CCCH is a forward link CDMA2000 channel that transmits control information to a specific mobile. The frame sizes for this channel may be one of the following lengths: 5, 10, or 20 mS which provide data rates of 9.6, 19.2, and 38.4 kbps respectively. When not on a call, mobile specific messages can be sent on the F-CCCH.
- Forward Broadcast Control Channel (F-BCCH): This CDMA2000 channel is used to broadcast messages to all mobiles within the coverage area of the cell. These messages may include advertisements of news as well as static paging messages. The channel transmits data at 4.8, 9.6, or 19.2 kbps.
- Forward Common Power Control Channel (F-CPCCH): Power control is an important element for any CDMA system as all mobiles should be received at around the same strength by the base station. To achieve this, the base station regulates the power of each mobile. Even when it is not involved in a call the mobile still needs to receive bits for its power control. Each mobile therefore monitors a particular bit in this CDMA2000 channel to enable it to adjust its power up or down by one increment. To ensure the maximum speed, this information is not encoded. If any data errors are introduced, the error is quickly corrected by the next bit.
- Forward Fundamental Channel (F-FCH): This CDMA2000 1X channel is still the main channel to carry the voice and data payload. The Forward Fundamental Channel uses a fixed amount of spreading and the variable data rates are achieved by using symbol repetition.
- Forward Supplemental Code Channel (F-SCCH): The Forward Supplemental Code Channels are retained from IS-95 and contained within a traffic channel, and they are used to carry voice or data, but may only be used with RC1 and RC2. For RC1 the frame size is 20 mS and the data rate is 9.6 kbps, whereas for RC2 the data rate is 14.4 kbps.
- Forward Supplemental Channel (F-SCH): This CDMA2000 channel is contained within the traffic channel and can only be used with Radio Configurations 3 to 5 for 1X and 6 to 9 for 3X. The channel can use variable length Walsh Codes to provide a constant spreading rate. It provides for a wide range of data rates from 1200 bps right up to 1036800 bps.
- Forward Dedicated Control Channel (F-DCCH): This channel carries information from the base station to the mobile. For IS-95 systems the control information was sent on the forward traffic channel along with the voice data during a call. The introduction of this CDMA2000 channel removes the requirement for the traffic channel to carry control information. This frees the traffic channel to carry the payload data for which it was primarily intended and this improves the efficiency of this CDMA2000 channel.
CDMA2000 reverse channels
Similar to the forward link there are many changes to the reverse link and the CDMA channels that are used to provide the improved performance and capabilities.
- Reverse Pilot Channel (R-PICH): This new channel for CDMA2000 provides a reference for base stations to gain initial access to a system and channel recovery. The channel also carries power control information for the forward link. Although the addition of this channel results in increased battery consumption, it provides significant advantages and has therefore been incorporated into the system.
- Reverse Access Channel (R-ACH): This channel operates in the same manner as that used for IS-95 and it provides backward compatibility. It is used by the mobile to transmit random bursts when it attempts to access the system.
- Reverse Enhanced Access Channel (R-EACH): The Reverse Enhanced Access Channel performs the same functions as R-ACH does in IS-95. It has been enhanced to provide improved access. There are two modes in which it can operate:
- The first is a basic access mode where the channel carries access messages in a similar manner to that used on IS-95.
- The second mode is termed a reservation access mode and it is used to reserve radio resources like Internet access etc.
- Reverse Common Control Channel (R-CCCH): This CDMA2000 channel is an access channel that enables CDMA2000 to provide improved packet access. It provides much faster access and the lower latency times required for packet access. It offers a 20 mS 9.6 kbps channel and in addition to this there are new 5 and 10mS frames that offer data rates of 19.2 and 38.4 kbps. As power levels are important, this CDMA2000 channel is controlled by a closed loop power control system.
- Reverse Dedicated Control Channel (R-DCCH): This CDMA2000 channel is similar to the F-DCCH. It is used to carry signalling and user information in a call for data traffic and as a result it is only present if there is data to be transmitted.
- Reverse Fundamental Channel (R-FCH): This is the channel in the reverse link that is used to carry the voice and data payload. It allows for either 5 or 20 mS frames, the shorter frames are used to give lower latency, i.e. the phone gets the data it needs in 5 ms rather than 20 ms.
- Reverse Supplemental Code Channel (R-SCCH): This channel is the equivalent of the F-SCCH and it is used with Radio Configurations 1 and 2. Again the timing of this channel is offset from the fundamental channel by 1.25 mS. There can be up to seven used per traffic channel.
- Reverse Supplemental Channel (R-SCH): The reverse supplemental channel provides user data rates that vary from as low as 1200 bps, up to 230.4 kbps (and 103.68 kbps for 3X). To accomplish this, the channel uses variable length Walsh codes. This channel only applies to Radio Configurations 3 and 4 for 1X and 5 and 6 for 3X.
It can be seen that there are many more CDMA2000 1X channels that channels included in IS-95. However these CDMA2000 channels assist in enabling CDMA2000 to provide much greater levels of flexibility, higher data rates, improved spectral efficiency and an overall better level of performance.
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