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weighting each bit by the inverse of the variance. This requires the variance to be measured on a

bit by bit basis, which significantly complicates the receiver. This is similar to the chip decision

used in SESS because a rake receiver uses a sequence of soft decision receiver outputs to make a

bit decision. If any of these soft decision receiver outputs have a large variance, much like the bit

decision used in SESS, it will greatly affect the output of the bit.

7.5 Summary

From this chapter it can be seen that noise or fading in a channel with jamming affects

the BER at lower SNR greatly. The effect at high SNR is less seen, which skews the worst-case

jamming, making it no longer an inverse relationship with the envelope of the curves. Chip

decision is a sub-optimal way that can be used to help fight the worst-case jamming conditions.

It does not always outperform bit decision, as in many conditions the bit decision remains the

better system. The worst-case jamming depends on prior knowledge of the system, the decision

to use chip based decisions requires knowledge of the jamming. With knowledge of the duty

cycle, a decision could be made to switch to chip based decision to help improve performance.

Another method employs using algorithms that readjust the weight of the chips at the equalizer,

known as least mean square algorithms. If the peak power of the jammer is limited it is going to

affect the jamming performance at low ρ in both chip and bit decision. The bottom line is that

without knowing the specifics of a jamming channel (i.e. capabilities of jammer, current jammer

state, etc.), it is very difficult to determine which model is superior.

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