Carrier Modulation; Multiplexing; Multiplexing In The Time Domain; Multiplexing In The Frequency Domain - Vectron HW 90196 User Manual

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User manual

Vectron

The frequency stability of the radio frequency carriers at the transceiver shall be better than +/- 50 kHz

under extreme temperature conditions.

10.4.2 Carrier modulation

For transmission of binary data on a frequency channel, GFSK modulation is used. The nominal modula-

tion equals 400 kHz. The modulation is performed on binary symbols (1 symbol = 1 bit). The symbol clock

equals 1.152 Mbit/s.

A transceiver may operate either as Basestation or as Endpoint of a radio network. A basic network com-

prises a single Basestation and multiple Endpoints. Communication happens always between an End-

point and a Basestation, i.e. there is no direct Endpoint-to-Endpoint communication.

Communication is based on connections. Establishing a connection means in fact the allocation of radio

spectrum resources for a specific link between an Endpoint and a Basestation. Multiple connections may

be active at the same time.

Moreover there is the requirement of sharing the radio spectrum with other low power devices operating

in the same band.

The radio spectrum is shared through a combination of time and frequency multiplexing.

The system used TDMA based on a 10ms time frame containing 11520 bit. The frame is divided into

K=24 time slots numbered k=0 to 23 in the order of transmission. Each time slot contains 480 bit. This

corresponds to a slot time of about 416,7 µs.

A connection is built by one or multiple bearers. A bearer is a sequence of transmissions occupying the

same time slot in a number of consecutive frames. Each transmission is a burst, starting with a preamble

followed by a synchronization word and payload data.

So a bearer is a sequence of burst transmissions. The duty cycle of a bearer is 1/24.

For the internal administration of the system a multiframe consisting of 16 frames and a superframe con-

sisting of 3 multiframes (i.e. N=48 frames) are defined. Each frame is numbered according to its position

in the superframe. Frame numbers range from n=0 to 47.

The system uses fast frequency hopping for multiplexing in the Frequency Domain. The hopping time, i.e.

the period between two consecutive hops, equals 10ms and is synchronized to the TDMA frame clock.

This frequency hopping scheme implies that consecutive transmissions for the same bearer always use

different frequency channels. The actual sequence of frequencies is defined by a so-called hopping pat-

tern.

A hopping pattern is a mapping of the frame number onto a corresponding frequency channel number.

Since the frame number is periodic with period N=48, also the hopping pattern is periodic with N=48.

Lin

02.02.2001

1.00

HW90195UserMan.doc

Subject to amendment, errors excepted

page 59/70

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