The frame period for 1xEV-DO is Each frame is divided up into 16 slots of 1. When compared to a voice communication system of cdma, the following design elements of the forward link contribute to raise the data rate:.
Full power - The cell is always at full power, resulting in no overhead needed for statistical variations of multiple users. Best serving cell - When in soft handoff, the mobile selects the best serving cell and can only request and receive data from that cell.
Efficient data delivery - The base station can send data to a mobile at times when its rate request is higher than the running average of the base station, and will avoid sending data when the requested rate is lower than the running average. The forward link is always transmitted at its full power, using a rate control scheme instead of a power control scheme, as in cdma The data is TDM time division multiplexed to the various users or mobiles, with only one being served at any time.
The base station decides which mobile should be served next. The maximum data transfer from the network will be achieved if only the most favorable links get served, however, this is accomplished at the expense of the distant users.
Traffic Channel - The data following the turbo coder is scrambled by mixing with a PN 1 part number, or 2 packet number sequence, the initial state of which is based on known parameters, and is unique for each user. At the same initial value of the PN sequence, every packet starts. QPSK modulation is used for data rate up to 1. Higher order modulation, with either 8PSK with 3 bits per symbol or 16QAM with 4 bits per symbol, is used for higher data rates.
The levels of the I and Q symbols are mathematically chosen so that the average power becomes 1. The I and Q channels are mapped into 16 parallel Walsh cover, each of length The I and Q outputs with the Walsh covers signals are added together.
Preamble - At the beginning of the transmission to one user, there is a preamble that is embedded in the data. This preamble contains the user ID for the data, and its repeat rate is determined by the data rate; lower data rates require higher repeat values. At its largest, the preamble will fill more than a half the first slot. The power control bits are sent in parallel to all mobiles with an open connection. Each one is assigned a different bit Walsh code which gets transmitted on either the I or Q channel.
The codes 0 through 3 are reserved. The Walsh code 4 is the RA cover. The Walsh codes 5 through 63 are allocated to RPC. One Walsh code is allocated for power control to each active reverse link. Power control bits for all of the reverse links are sent in parallel as part of the MAC channel.
These are made of 4 repetitions of an assigned Walsh code of length The RA channel is used to indicate that the sector is busy decoding multiple reverse link signals.
Pilot - The pilot signal is gated on for only chips per slot. The differentiator between cells and sectors is still the PN offset of the pilot channel. The reverse link for 1xEV-DO has a structure similar to that for cdma, except that in addition to a data channel, the following channels are also included:.
Reverse Rate Indication RRI - This replaces with the power control bits to indicate of which data rate is requested by the mobile. Data Request Channel DRC - This contains a 4-bit word in each slot to allow the choice of up to 16 different transmission rates. Different Walsh covers are used to indicate which PN offset in the active set is preferred for transmission.
Ack Channel - This acknowledgement channel is only transmitted after the mobile detects a frame with its preamble, meaning the packet is directed to that mobile. All models feature improved battery life, display, cameras, and processor. While the price is certainly right, are they truly a good value, or just cheap? It's not a flagship, but it's well above the usual affordable fare that Motorola has primarily focused on in recent years.
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