M-LEVEL ENCODER

(m-QAM & m - PSK CONSTELLATION GENERATOR)

MULTI-LEVEL ENCODER SECTION GUIDE

A continuous sequence of TTL-level data bits is grouped into sets of 'L' bits, (where L = 2, 3 or 4). Each set of 'L' bits is encoded to form a pair of M-level baseband signals, q & i .

This q & i signal pair can be represented as 2^L unique points (or symbols) in a signal-state-space diagram, or constellation.

Six different encoding formats are available, selected via front panel switches, for generating 4-QAM, 8-QAM, 16-QAM, 4-PSK, 8-PSK & 16-PSK signals.

A 'demonstration' mode for viewing constellation displays is also provided.

USE

OPERATING MODES

Two operating modes are provided, NORMal and DEMO. The PCB mounted jumper, J3 is used to set the operating mode.

NORMal mode provides full functional operation of the module. Both DATA and CLK input signals are required for normal operation.

DEMO mode has limited functional application. It is used only for self test and illustration purposes, to allow the quick setting-up of a constellation display on an oscilloscope. Only a clock signal at the CLK input is required: the DATA input is unused.

INPUT SIGNALS

Two TTL level input signals are required for normal operation: DATA and CLK. The DATA input signal must be synchronised and in-phase with the CLK signal.

CONSTELLATION SELECT

Two front panel CONSTELLATION SELECT switches are used to choose the encoding format required. The upper, 2 position switch selects between either a circular (phase) or square
(amplitude) array. The lower, 3 position switch selects the number of points in the constellation: 4, 8 or 16.

The following table lists switch settings required for generating the six available constellations.

Front Panel Switches		Constellation Selected
Upper	Lower
	4-point	4-PSK
	8-point	8-PSK
	16-point	16-PSK

Front Panel Switches		Constellation Selected
Upper	Lower
	4-point	4-QAM
	8-point	8-QAM
	16-point	16-QAM

The Space Diagrams for the above constellations are shown below,

OUTPUT SIGNALS

Two multi-level analog signals are output, labeled q_branch and i_branch. The number of discrete M-levels and the voltage difference between each level is determined by the front panel CONSTELLATION SELECT switch settings. See the table below.

Front Panel Switches		Number of M-levels at i & q
Upper	Lower
	4-point	3
	8-point	4
	16-point	8

Front Panel Switches		Constellation Selected
Upper	Lower
	4-point	2
	8-point	4
	16-point	4

For each of the six available settings, the peak-to-peak amplitude of the q_branch and i_branch signals will always be ±2.5V.

BASIC SPECIFICATIONS

DATA Input serial, TTL-level

CLK Input up to 10kHz, TTL-level

OPERATING MODES PCB jumper selectable

NORM converts sets of input DATA into pairs of multi-level signals

DEMO for testing and displaying constellations only

CONSTELLATION SELECT front panel switch selectable, offering either circular or rectangular, 4, 8 and 16 point constellations

i_branch & q_branch Outputs 2, 3, 4 or 8 level, depending upon constellation selected, ± 2.5V _pk-pk

TECHNICAL DETAILS

The signal-state-space diagrams for the six available constellations follow. Note that the data bits representing each symbol are arranged in a Grey Code sequence.

When viewing the above constellations on an oscilloscope, it is important to note that the horizontal axis in the above diagrams is i and the vertical axis is q.

HINT: To assist in determining the correct orientation of the viewed constellation, presenting a logical high to the DATA input of the M-LEVEL ENCODER module (e.g. press the RESET push button on the SEQUENCE GENERATOR module), will only display the 11, 111 or 1111 symbol, depending upon the constellation selected.

QUICK OPERATION GUIDE

1. DEMO Mode
1. Set PCB mounted jumper, J3, to DEMO position.
2. Connect a TTL clock to the CLK input. For example use the 8.3kHz from the MASTER SIGNALS module.
3. Select the constellation required via the front panel switches.
4. View the qbranch and ibranch output signals on an oscilloscope, in XY mode.
2. NORMal Mode with SEQUENCE GENERATOR module
1. Set PCB mounted jumper, J3, to NORM position.
2. Plug the SEQUENCE GENERATOR and M-LEVEL ENCODER modules into the TIMS rack.
3. Connect a TTL clock to both modules' CLK input. For example use the 8.3kHz from the MASTER SIGNALS module.
4. Patch the SEQUENCE GENERATOR module's TTL level X output to the M-LEVEL ENCODER module's DATA input.
5. Select the constellation required via the front panel switches.
6. View the q_branch and i_branch output signals on an oscilloscope, in XY mode.
3. M-QAM & M-PSK Generation
1. Follow steps 1 to 6, as described in section B above, and then patch together two MULTIPLIER and an ADDER module as illustrated below.

m-QAM & m-PSK Generator Block Diagram

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