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AMRT > Beach Example 2 > Flashcards

Beach Example 2 Flashcards

1
Q

Adaptive Antenna Definition

A

a multi-element antenna w/ a BF capable of adjusting / controlling the beam pattern of the antenna system in terms of main beam + null placement + sidelobe control

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2
Q

Benefits of cap, service (bit rate) + range enhancement from an adaptive antenna system? (4)

A
  • Both SFIR + SDMA used to incr. network cap
  • Single Antenna array system, impact of delay spread can also be reduced
  • Higher data rate services offered for non-eq. systems
  • Range extension can be obtained by aligning the array gain in the direction
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3
Q

Differences between fixed + fully adaptive BF? (2)

A

Fully Adapt. - full complex weights

Fixed - similar to the grid of beams / Aalborg Alg.

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4
Q

Why is transmit BF a problem in FDD systems?

A

UL + DL will experience freq. selective fading

—> exhibit different power azimuth spectrum

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5
Q

Adaptive Control Alg. (5)

(GMMOA)

A

Grid of Beams - GoB

Maximal Ratio Combining - MRC

Music Based Beam Synthesis - MUS

Optimum Combining - OPT

Aalborg Alg. - AUC

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6
Q

Grid of Beams (3)

A
  • 13 fixed beams (10 degree intervals from -60 to 60 in azimuth) are synthesised by the BF
  • Beam w/ highest o/p power is selected for reception
  • Same look direction is used for the transmit case
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7
Q

Maximal Ratio Combining (2)

A
  • performs maximum ratio combining on UL + uses same weight vector for DL
  • Maximises SNR @ combiner by co-phasing the array signals + weighting them according to their ​SNR
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8
Q

Music Based Beam Synthesis

A

Super resolution DoA alg. is used to identify src locations and drive BF

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9
Q

Optimum Combining (2)

A
  • Training codes are used as a reference signal to compute the Wiener optimum weight vector
  • Minimising the error signal between the reference + weighted o/p array
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10
Q

Aalborg Alg. (2)

A
  • 22 beams formed over 120 degrees
  • Beam w/ highest correlation w/ the training seq is selected for both reception + Tx
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11
Q

Control Alg. used in large/small cell deployment

A

Large - Spatial Reference (DoA then BF)

Small - Optimum Combiner

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12
Q

Temporal Reference BF

A

appl of a training seq w/ a high correlation to the wanted signal

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13
Q

How does MIMO provide a capacity enhancement over conventional systems? (2)

A
  • MIMO facilitates the stimulation + reslutions of multiple orthogonal spatial channels
  • Channels can convery truly parallel info bearing waveforms @ same time + freq
    • incr. info cap. compared to a SISO system
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14
Q

Property of MIMO channel for a cap. enhancement?

A

multipath richness leading to a full rank H matrix

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15
Q

Potential capacity gains from using MIMO? (3)

A
  • scales linearly w/ # antennas for a square
  • Assume IID Rayleigh channel
  • e.g. 4x4 = x4 gain
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16
Q

Why are the gain of the eigenvalues important when assessing the cap of MIMO system?

A

eigen values specify the individual gains of the orthogonal spatial channels + their ability to carry info

17
Q

Waterfilling definition (2)

A
  • A practical MIMO channel will have different eigen channel gains
  • Load high gain channels w/ more info
    • i.e. waterfilling, greater capacity can be achieved
18
Q

How is Waterfilling achieved? (3)

A
  • Feedback used to access CSI
  • Rx observes + feeds this back to Tx
  • Tx adjusts mod + coding rates to match
19
Q

How can # spatial channels be determined from the equipment config + channel parameters?

A

Max # spatial channels = min # of:

  • Tx antennas
  • Rx Antennas
  • Scatters in environment
20
Q

Why does the offered cap. of individual spatial channels vary in a practical deployment of a MIMO system? (2)

A

Offered cap. of a MIMO syst is lower due to:

  • channel correlation
  • lower eigen channel gains
21
Q

Spatial Multiplexing definition (2)

A
  • individual spatial channels carry a part of the message + recombine @ Rx
  • sum cap. is sum of the individual orthogonal spatial channels
22
Q

Space-Time Code Definition (3)

A
  • Transmitted waveform is coded over both space + time = diversity
  • Diversity reception can also be employed
  • Provides robust transmission + no capacity expansion
23
Q

Differences between Spatial Multiplexing + Space-Time Coding (2)

A

SM - provides throughput enhancement, but needs high SNR for signal separation

STC - provides good BER / outage performance @ low SNR

24
Q

Massive MIMO defintion

A

A MIMO system w/ >50 . antennas @ AP / BS serving a multi-user MIMO network w/ 10 users

25
Q

Why is TDD based interface best suited to Massive MIMO?

A

estimates from the UL can be directly applied to the DL gain given the the channel is reciprocal

26
Q

Why is ZF > MRT in Massive MIMO (2)

A
  • ZF directly exploits channel spatial structure
  • MRT can be confused by closely correlated spatial signatures

AMRT (8 decks)

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