Beach Example 2 Flashcards
Adaptive Antenna Definition
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
Benefits of cap, service (bit rate) + range enhancement from an adaptive antenna system? (4)
- 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
Differences between fixed + fully adaptive BF? (2)
Fully Adapt. - full complex weights
Fixed - similar to the grid of beams / Aalborg Alg.
Why is transmit BF a problem in FDD systems?
UL + DL will experience freq. selective fading
—> exhibit different power azimuth spectrum
Adaptive Control Alg. (5)
(GMMOA)
Grid of Beams - GoB
Maximal Ratio Combining - MRC
Music Based Beam Synthesis - MUS
Optimum Combining - OPT
Aalborg Alg. - AUC
Grid of Beams (3)
- 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
Maximal Ratio Combining (2)
- 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
Music Based Beam Synthesis
Super resolution DoA alg. is used to identify src locations and drive BF
Optimum Combining (2)
- 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
Aalborg Alg. (2)
- 22 beams formed over 120 degrees
- Beam w/ highest correlation w/ the training seq is selected for both reception + Tx
Control Alg. used in large/small cell deployment
Large - Spatial Reference (DoA then BF)
Small - Optimum Combiner
Temporal Reference BF
appl of a training seq w/ a high correlation to the wanted signal
How does MIMO provide a capacity enhancement over conventional systems? (2)
- 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
Property of MIMO channel for a cap. enhancement?
multipath richness leading to a full rank H matrix
Potential capacity gains from using MIMO? (3)
- scales linearly w/ # antennas for a square
- Assume IID Rayleigh channel
- e.g. 4x4 = x4 gain
Why are the gain of the eigenvalues important when assessing the cap of MIMO system?
eigen values specify the individual gains of the orthogonal spatial channels + their ability to carry info
Waterfilling definition (2)
- 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
How is Waterfilling achieved? (3)
- Feedback used to access CSI
- Rx observes + feeds this back to Tx
- Tx adjusts mod + coding rates to match
How can # spatial channels be determined from the equipment config + channel parameters?
Max # spatial channels = min # of:
- Tx antennas
- Rx Antennas
- Scatters in environment
Why does the offered cap. of individual spatial channels vary in a practical deployment of a MIMO system? (2)
Offered cap. of a MIMO syst is lower due to:
- channel correlation
- lower eigen channel gains
Spatial Multiplexing definition (2)
- individual spatial channels carry a part of the message + recombine @ Rx
- sum cap. is sum of the individual orthogonal spatial channels
Space-Time Code Definition (3)
- Transmitted waveform is coded over both space + time = diversity
- Diversity reception can also be employed
- Provides robust transmission + no capacity expansion
Differences between Spatial Multiplexing + Space-Time Coding (2)
SM - provides throughput enhancement, but needs high SNR for signal separation
STC - provides good BER / outage performance @ low SNR
Massive MIMO defintion
A MIMO system w/ >50 . antennas @ AP / BS serving a multi-user MIMO network w/ 10 users
Why is TDD based interface best suited to Massive MIMO?
estimates from the UL can be directly applied to the DL gain given the the channel is reciprocal
Why is ZF > MRT in Massive MIMO (2)
- ZF directly exploits channel spatial structure
- MRT can be confused by closely correlated spatial signatures
