Forward channels carry information from Base Station to Mobile station. These channels are of two types, Dedicated channels and Control channels. Forward dedicated channels carry information between the base station and a specific MS. Common channels carry information from the base station to a set of mobiles in a point-to-multipoint manner.

Below table lists these channels.

In this section, the functions of those channels which are not present in IS 95 are presented.

• Forward Common Control CHannel (F-CCCH): The F- CCCH is a forward link CDMA2000 channel that transmits control information to a specific user. The frame sizes for this channel may be one of the following lengths: 5, 10, or 20 ms which provides data rates of 9.6, 19.2, and 38.4 Kbps respectively. When not on a call, user specific messages can be sent on the F-CCCH.
• Forward Quick Paging CHannel (F-QPCH): This channel provides information to the user 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 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 Auxiliary Transmit Diversity Pilot Channel (F-ATDPICH): This CDMA 2000 channel is required when transmitting diversity in each beam when using a smart antenna system.
• Forward Common Power Control Channel (F-CPCCH): Power control is an important element for any CDMA system as all users’ signal should be received of the same strength at the Base Station. To achieve this, the Base Station regulates the power of each user. Even when the user is not making a call, it still needs to receive bits for its power control. Each user therefore monitors a particular bit in this CDMA 2000 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 Broadcast Control Channel (F-BCCH): This CDMA 2000 channel is used to broadcast messages to all users 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 Dedicated Control Channel (F-DCCH): This channel carries information from the Base Station to the user. 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 CDMA 2000 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 CDMA 2000 channel.
• 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 Traffic Supplemental Channel (FT-SCH): This CDMA 2000 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 Link Features: The forward link supports chip rates of N x 1.2288 Mcps (where N= 1, 3, 6, 9, 12). For N = 1, the spreading is similar to IS-95 B; however, QPSK modulation and fast closed loop power control are used. For chip rates with N >1 the multicarrier (see Figure 26) option is used. The multicarrier approach demultiplexes modulation symbols onto N separate 1.25 MHz carriers (N = 3, 6, 9, 12). Each carrier is spread with 1.2288 Mcps rate.

(i)Transmit Diversity: Transmit diversity can reduce the required Eb/N0 (or required transmit power per channel) and thus enhances the system capacity. Transmit diversity can be implemented in the following ways:

Multi-carrier Transmit Diversity: In a 3 X 1.25 MHz multicarrier transmitter, the serial coded information symbols are divided into three parallel data streams, and each data stream is spread with a Walsh code and a long pseudo-random noise (PN) sequence at a Rate of 1.2288 Mcps. After processing, the parallel serial coded information symbols with a carrier are transmitted by three antennas. It is called multi-carrier transmit diversity (MCTD). At the output of the transmitter, there are three carriers: A, B, and C (see Figure 27). Frequency filtering provides perfect orthogonality between antennas. Hence improved frequency diversity and increase in forward link capacity is achieved.

(ii)Orthogonal Modulation: To reduce or eliminate intracellular interference, each forward link physical channel is modulated by a Walsh code. To increase the number of usable Walsh codes, quadrature phase shift keying (QPSK) modulation is used before spreading. Every two information bits are mapped to a QPSK symbol. As a result, the available number of Walsh codes is increased by a factor of two, relative to binary phase shift keying (BPSK) (prespreading) symbols. Walsh code length is varied to achieve different information bit rates.

(iii)Power Control: The forward link power control in 3G is fundamentally different from IS 95. Its main objective is to increase the voice call capacity in the forward link by a series of new enhancements, including: high speed forward power control, closed loop with fast time response and variable power step size controlled by the BS.

The forward link power control: In this section the power control techniques on forward link is described.

(a)High speed forward power control: The link is characterized by fast Rayleigh fading,

• To track and compensate it accurately the power control operates at a high rate on the forward link.

• The accurate tracking minimizes the average power transmitted by the BS to the mobile and, as a consequence, increases the forward link call capacity.

• The rate of the forward link power control is increased by replacing the slow FER-based algorithm of IS-95 with a closed loop based on Eb/Nt measurements. These measurements are performed at a subframe interval. This allows the 3G forward link power control to operate at high speed.

• The increase in forward link capacity is expected mostly for users moving at low speed and in simplex mode (i.e., not in soft handoff) where fast Rayleigh fading can be tracked and mitigated effectively.

• For users travelling at high speed, the fast power control cannot track the fast Rayleigh fading accurately, and, therefore, a large increase in capacity may not be expected.

(b)Variable power step size controlled power control:

The variable power step size has not been standardized in CDMA-2000, and therefore the BS has the flexibility to adapt the step size depending on the speed of the user and soft handoff status of the call. This adaptability permits minimization of the peak to average power ratio, and decreases the overall interference, which increases the forward link capacity.

(c)Closed loop with fast time response:

The standards specify a fast closed loop power control at 800 Hz. Two schemes of power control for the F-FCH and F-SCH have been proposed in CDMA 2000.

• Single Channel Power Control: This is based on the performance of the higher rate channel between the F-FCH and F-SCH. The gain setting for the lower rate channel is specific deployment and operating environment. When a Walsh code limit occurs, additional codes may be generated by multiplying Walsh codes by the masking function.
• Independent Power Control: In this case, gains for the F-FCH and F-SCH are determined separately. The mobile runs two separate outer loop algorithms (with different $E_{b}/N_{t}$ targets) and sends two forward error bits to the Base Station.