Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

AMRT > 2016 Exam > Flashcards

2016 Exam Flashcards

1
Q

Advof Iterative alg. LMS + RLS in comp to direct calc. ZF + MMSE (3)

A
  • Iterative alg. enable computational load of calculating the co-effs to be spread over multiple symbol periods (each symbol of training seq)
  • Dir calc. can only be implemented @ end of seq
  • Needs al computation completed in a very short time, incr. peak computational load
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Traceback Length for compr. between compl. + eq. performance

A

Traceback over 5L,

5x longer than the constraint length (L+1)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Freq. Hopping Definition

A

instantaneous carrier freq. is changed periodically to a new value by means of a hopping sequence.

Carrier is hopped over a much larger b/w than info signal

(appl - BT)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Direct Sequence Definition

A

narrowband info signal is spread to a wider b/w waveform by directly modulating w/ a wideband SS

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Spreading Code Generation

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Mathematical property of gnerator polynomial to ensure good op. cond.?

A

Needs to be a primitive polynomial

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Range Extension Definition

A

incr. gain offered by the array over a single element antenna yields an incr. in the cell radius / coverage area

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Spatial Filtering for Interference Reduction (SFIR) (2)

A
  • smart antenna focuses energy at an addr. volume, thereby reducing both interference ‘caused by’ as well as ‘seen by’ the wireless channel
  • co-channel interference is reduced
    • re-use distances can be reduced
      • incr. network cap.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

SDMA Definition

A

supports time, freq + code re-use through the spatial separation of users within the same cell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Why are TDD air based interfaces suited to Massive MIMO?

A

Massive MIMO can exploit channel reciprocity in order to derive the transmit vector (pre-coding) directly from the UL

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Why are values w-2 + w-1 intuitively obvious?

A

Both are zero because zero forcing causes all terms to be estimated except for the kth symbol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Why is ZF only approx + change required for accuracy?

A

ZF only approx due to only 2x eq. taps used to cancel 2x post cursor taps

–> Significantly more taps required in order to approach exact ZF

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Merits of incr/decr GI (3)

A
  • incr GI allow more tolerance for timing, but reduces eff.
  • Good choice if timing synch. is an issue + large mod. order (64-QAM)
  • decr. GI results in some ISI but incr. eff. - good for low order mod + robust to ISI
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How can narrow-band + wide-band interference be suppressed?

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Extended anaylsis for a multi-user CDMA DS-SS

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Why is Pwr Control required for multiple user operation? (2)

A

BS receiver only separates users by means of their spreading codes

A user far from the BS will be swamped/saturated with a close user’s waveform –> unable to detect anything far away

17
Q

How is Power Control implemented in 3G cellular for FDD? (4)

A
  • Freq. selective fading on UL + DL is decorrelated, so both UL & DL pwr control is necessary
  • Av path loss + shadowing is estimated by OL controller based on received signal strength @ mobile
  • BS corrects for the freq. selective, uses CL info channel, instructing mobile to adjust transmit power
  • 1-bit Delta Sigma control can be employed for CL pwr control to save b/w

- incr. the update rate by using multi-bit power control or a wider spreading b/w (more freq. diversity = less power errors)

18
Q

Which paramters have the greatest impact on the channel capacity

A

nT scales the transmit pwr, so total energy is the same when making comparisons

HH* describes the orthogonality of teh spatial channels

SNR has biggest impact on channel capacity

19
Q

What can be inferred regarding spatial channel structure + offered information capacity (2)

A
  • individual Eigen channel gains + info bearing capacity of the spatial streams can be observed
  • Checking to see if system is full rank
    • i.e. all channels convey data
20
Q

Min # of MIMO Channel

21
Q

Why are channel gains of a MIMO system different?

A

Due to multipath structure combined w/ antenna response

22
Q

How to exploit info @ Tx in MIMO?

A

If CSI is known @ Tx, waterfilling can be applied to maximise the capacity of the strong eigenvalues + reduce the impact of weaker channels

23
Q

How do singular values of the massive MIMO channel gain matrix vary + impact on signal processing (2)

A
  • become well-conditioned or deterministic
  • Matrix inversion becomes simpler
24
Q

Channel Hardening definition

A

large numbers of high levels of spatial diversity reducing fast fading

25
Q

What are Pilots used for?

A

Used in channel est.

26
Q

Cause of Pilot Contamination

A

Will be re-used in adj. cells, causing interference + limiting the operation of massive MIMO

AMRT (8 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions