TEDS is based on variable subcarrier/channel bandwidths of 25, 50, 100, and 150kHz, with burst uplink and continuous downlink slot formats. In particular, the Normal Downlink, Normal Uplink, and Control Uplink slot formats feature a 25kHz channel bandwidth with 8 subcarriers; a 50kHz channel bandwidth with 16 subcarriers; a 100kHz channel bandwidth with 32 subcarriers, and a 150kHz channel bandwidth with 48 subcarriers, while the Random Access only applies to a 25kHz channel bandwidth with 8 subcarriers.
The following tables describe the common modulation parameters and parameters specific to each of the slot formats:
Additional topics in this section include the following:
Parameter 
Description 

RF Subcarriers 
8 (25kHz channel bandwidth) 



16 (50kHz channel bandwidth) 



32 (100kHz channel bandwidth) 



48 (150kHz channel bandwidth) 
Subcarrier Spacing 
2.7kHz 
Subcarrier Symbol Rate 
2400sym/s 
Symbol Filter 
Root Raised Cosine (RRC) (alpha = 0.2) 
Demodulation 
Coherent (Pilot Symbol Assisted) 
Frame Rate 
32 Slots/Frame 
Slot Interleave 
Variable 
The following are parameters that are specific to the different slot formats.
Parameters 
TEDS Modulation Slot Formats 


Normal Downlink 
Normal Uplink 
Random Access 
Control Uplink  
25, 50, 100, and 150kHz 
25, 50, 100, and 150kHz 
25kHz only 
25, 50, 100, and 150kHz 

4QAM, 
4QAM, 
4QAM 
4QAM, 

Minimum Search Length 
14.167msec (85/6 ms) 
14.167msec (85/6 ms) 
7.083msec (85/12 ms) 
7.083msec (85/12 ms) 
Use PvT Off Analysis Time with the minimum Search Length values in the table above to determine the smallest values you can enter for Search Length.
The modulation selected for TEDS delivers a flexible bit rate in a 25kHz/50kHz/100kHz/150kHz radio channel bandwidths. The basic mode of operation for TEDS is TDMA. The downlink transmission mode is continuous, while the uplink transmission mode is pulsed on a slot by slot basis. Layer 1 reserves certain symbols within the information stream to provide for its operation. These reserved symbols synchronize the radio channel and provide a known reference for performing coherent demodulation of the subcarriers.
TEDS is a format within the family of Multiple Quadrature Amplitude Modulation (MQAM) formats. MQAM are distinguished by multiple carriers of standard digital modulation, with each carrier called a subcarrier or subchannel. Each subcarrier is generated digitally, thus all subcarriers are coherent, plus each subcarrier is filtered independently using a Root Raised cosine (RRC) filter with a shape factor (alpha) of 0.2 (adjustable). Note that subcarriers are not orthogonal in frequency, thus MQAM is not Orthogonal Frequency Division Multiplexing (OFDM). The MQAM formats for TEDS are 4QAM (QPSK) (4 states with 2 bits per symbol), 16QAM (16 states with 4 bits per symbol), and 64QAM (64 states with 6 bits per symbol).
TEDS features a variable number of subcarriers with corresponding variable channel bandwidths:
Channel Bandwidth 
Number of subcarriers 

150kHz 
48 (24 to 24) 
100kHz 
32 (16 to 16) 
50kHz 
16 (8 to 8) 
25kHz 
8 (4 to 4) 
Subcarriers are separated by 2.7kHz and centered about the center frequency. Subcarriers are designated negative () or positive (+) of the center frequency, for example: 4 to 1 and +1 to +4 for an 8 subcarrier. The following images show you an 8 subcarrier designation.
The number of symbols in each subcarrier depends on the slot format selected. The table below shows the relationship of symbols to each slot format.
Slot Format 
Number of symbols (per subcarrier) 

Normal Uplink 
31 
Normal Downlink 
34 
Random Access 
14 
Control Uplink 
14 
The number of bits in each symbol depends on the modulation type selected. The following table shows the relationship of bits to each modulation type.
Modulation Type 
Number of bits (per symbol) 

4QAM 
2 
16QAM 
4 
64QAM 
6 
Each TEDS subcarrier uses a Root Raised Cosine (RRC) filter to process the output of the corresponding subcarrier symbol generator at the transmitting end. The RRC filter ensures minimal system intersymbol interference and maximum frequency domain attenuation outside the subchannel bandwidth, which minimizes interference to adjacent subcarriers. The RRC filter is characterized by the excess bandwidth factor (rolloff coefficient), alpha.
An ideal "brickwall" filter results in an occupied bandwidth that is equal to the symbol rate, in this case, an occupied bandwidth of 5.4kHz (alpha = 0). However, this is not practical because of the rolloff characteristic of the filter. The filter alpha is calculated in the frequency domain by comparing the RRC frequency at the 50% signal attenuation point (W0) to the 100% signal attenuation point (W) using: [W = (1 + alpha) W0] where W0= 2400Hz and W=2880Hz, yielding alpha = 0.2.
See Root Raised Cosine Filter in the Digital Demod section for more information.
TEDS analysis supports the following modulation types:
See Also
Overview of Slots and Symbols (TEDS)
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