LG GoldStream LW1100P Manual page 8

and the data and /or header are modulated differently. The modulator can support date rates of 1, 2,
5.5 and 11Mbps. The programming details to set up the modulator are given at the introductory
paragraph of this section. The HFA3861B utilizes Quadraphase (I/Q) modulation at baseband for all
modulation modes. In the 1Mbps DBPSK mode, the I and Q Channels are connected together and
driven with the output of the scrambler and differential encoder. The I and Q Channels are then both
multiplied with the 11-bit Barker word at the spread rate. The I and Q signals go to the Quadrature
upconverter (HFA3724) to be modulated onto a carrier. Thus, the spreading and data modulation are
BPSK modulated onto the carrier.
For the 2Mbps DQPSK mode, the serial data is formed into dibits or bit pairs in the differential
encoder as detailed above. One of the bits from the differential encoder goes to the I Channel and
the other to the Q Channel. The I and Q Channels are then both multiplied with the 11-bit Barker
word at the spread rate. This forms QPSK modulation at the symbol rate with BPSK modulation at
the spread rate.
- Transmit Filter Description
To minimize the requirements on the analog transmit filtering, the transmit section shown in Figure 11
has an output digital filter. This filter is a Finite Impulse Response (FIR) style filter whose shape is set
by tap coefficients. This filter shapes the spectrum to meet the radio spectral mask requirements while
minimizing the peak to average amplitude on the output. To meet the particular spread spectrum
processing gain regulatory requirements in Japan, an extra FIR filter shape has been included that
has a wider main lobe. This increases the 90% power bandwidth from about 11MHz to 14MHz. It has
the unavoidable side effect of increasing the amplitude modulation, so the available transmit power is
compromised by 2dB when using this filter (CR 11 bit 5). The receive section Channel Matched Filter
(CMF) is also tailored to match the characteristics of the transmit filter.
2.8 Wireless LAN Medium Access Controller(HFA3841)
The HFA3841 is designed to provide maximum performance with minimum power consumption.
External pin layout is organized to provide optimal PC board layout to all user interfaces. Firmware
implements the full IEEE 802.11 Wireless LAN MAC protocol. It supports BSS and IBSS operation
under DCF, and operation under the optional Point Coordination Function (PCF). Low level protocol
functions such as RTS/CTS generation and acknowledgement, fragmentation and de-fragmentation,
and automatic beacon monitoring are handed without host intervention. Active scanning is performed
autonomously once initiated by host command. Host interface command and status handshakes allow
concurrent operations from multi-threaded I/O drivers.
LG GoldStream