# Presentation: 317625

## Space Time Processing for Fixed Broadband Wireless

**A. Paulraj**
**Gigabit Wireless**
**&**
**Stanford University**
**ISART **
**6 -8 September, 2000 **
**Boulder, CO**

## Essential Attributes of Broad Band Wireless (BWA) Network

- High Speed > 4-5 Mbps
- High QoS / Availability
- DSL / Cable like
- Low Costs $$$
- High capacity
- High coverage
- CPE and Infrastructure unit costs
- Friendly
- Easy CPE Install
- Environmental/Regulatory
- Scalability (Multi-cell)
- Evolution to portability

## BWA Network Architecture

- Multi-cell architecture
- Low BTS antennas (50 - 150 ft)
- Under-the-eave subscriber antennas
- Significant Non-LOS propagation (Rayleigh fading)
- Strong multi-path
- Low Doppler channels

- Mobile cellular-like network with all its challenges but with 50 Speed and 50 QoS** **

## BWA Network

**NAU****	****= Network Access Unit**
**BTS ****	****= Base Transceiver Station**
**BSC ****	****= Base Station Controller**

**BWA Network**

**NAU**

- IP

**NGU**

**BSC**

**BTS**

**BTS**

**BTS**

**Voice gateway**

**Network Operations Center**

**SMS**

**Access Mux**

**IP**
**Gateway**

**NAU**

**NGU****	****= Network Gateway Unit**
**SMS****	****= Subscription Management System**

## Data Rate & QoS Challenges

** ******50 High Data Rate

-  50 QoS
- 	(0.999 Availability on
- 	Throughput, Delay, Jitter)

- Capacity
- 	(Bits/Hz/Cell)

- Coverage
- 	(Cell Radius)

- 0.4

- 0.2

- 0.4

## Typical Propagation Scenario

**Typical Propagation Scenario**

- BTS Directional Antenna

- BTS

- Ht  30’-150’

- Ht  8’-20’

- 0.1 - 5 miles

- CPE Directional Antenna

- Distance to mobile scatterers

## Path Loss (Mean Level)

**Path Loss (Mean Level)**

- Signal Power (dB)

- Super Cell
- BTS ht: 1500ft

- Macro Cell
- BTS ht 150 ft

- Range in km

- Frequency: 2.5 GHz
- Ant Beamwidth: 90 deg

- Super Cell: Free Space model
- Macro/Micro Cell: Erceg’s model

## K-Factor vs. Distance (Suburban BWA)

- ht = 15m, 90 deg. Rx antenna

- hr = 3m

- hr = 10m

**GW and AT&T **
**measured data similar**

**K = 0 is necessary assumption for reliable deployment**

**  ****---**** ****hr = 10m**** **
**--- ****hr = 3m**

## RMS Delay Spread vs Distance (Suburban BWA)

- RMS Delay Spread in Microseconds (dB)

- Distance in km

**GW experimental **
**data similar**** **

## Doppler Spectrum - BWA

- - 3dB

- fmax

- 

- 0.05  fd 0.5 Hz

## Signal Measurements

- Low Doppler, 0.05 Hz

- High Doppler, 0.5 Hz

## C vs I Measurements

## MIMO Measurements

- BTS

- CPE

- H22

- H12

- H21

- H11

## Spatial Multiplexing (SM) Offers Higher Speeds

- Each Eigen mode of the matrix channel can support a radio link. 11.4  1.5 speed up possible in 2 x 3 systems.

- Tx

- Rx

- H

## Increasing Capacity/Coverage

- Coverage: Lower the C/N needed to close link - improves link budget
- Capacity: Lower C/I needed to close link - improves reuse factor
- Use diversity, array gain, coding, etc to minimize required C/N or C/I to support a target PER
- Use RLP and fragmentation to allow higher target PER
- Use spatial multiplexing to run parallel channels

## Throughput vs Utiliz. (vs PER)

- 0

- 0.1

- 0.2

- 0.3

- 0.4

- 0.5

- 0.6

- 0.7

- 0.8

- 100

- 120

- 140

- 160

- 180

- 200

- 220

- Mode 6, Doppler 1Hz, MaxUtil 635 users, small files

- link utilization [%]

- mean throughput [Kbps]

- Mean Per 1%

- Mean Per 5%

- Mean Per 10%

- 0

- 0.1

- 0.2

- 0.3

- 0.4

- 0.5

- 0.6

- 0.7

- 0.8

- 0

- 500

- 1000

- 1500

- 2000

- 2500

- 3000

- Mode 6, Doppler 1Hz, MaxUtil 635 users, big files

- link utilization [%]

- mean throughput [Kbps]

- Mean Per 1%

- Mean Per 5%

- Mean Per 10%

- - TCP windowing algorithm yields the difference in the   throughput of ‘small’ and ‘big’ files

- - Throughput = File size/ Mean transfer delay

**Throughput vs Utiliz. (vs PER)**

## Increasing Coverage

- Diversity is critical (Tx antenna, Rx antenna, frequency, pol)
- Directional CPE antennas
- Forward Error Correction (FEC) & ARQ
- Increase BTS & CPE height

## Coverage vs Required C/N

- 0

- 5

- 10

- 15

- 20

- 25

- 30

- 1

- 2

- 3

- 4

- 5

- 6

- 7

- 8

- Range in Miles

- 1 x 1, NO RLP

- 2 x 2, RLP

-        Required C/ N

## CDF of Tx-Rx Diversity - Measured Data

- -40

- -30

- -20

- -10

- 0

- 10

- 20

- 10

- -4

- 10

- -3

- 10

- -2

- 10

- -1

- 10

- 0

- Signal Power About Mean in dB

- Probability That Signal Power < Abscissa

**Before Combining**

**After Combining**

**1 x 2**

**2 x 2**

- Probability of signal falling 10 dB below mean is 300 times lower with 2 x 2 compared 1 x 1

## Increasing Spectrum Efficiency

** **Reduce CCI to improve reuse
** ****-**** **Increase signal diversity
-  - Interference averaging
-  - Antenna sectorization, beam forming, interference cancellation
** **Reduce ACI to improve reuse** **
** **- Careful frequency planning
-  - Stringent emission masks, Rx filtering
-  - Interference suppression
** **Use link adaptation to exploit available C/N or C/I
-   levels
-  Use Radio Link Protocol to allow link to use high
-   BER

## C/ I After Combining - Measured Data

**C /I = 10 dB**

- -40

- -30

- -20

- -10

- 0

- 10

- 20

- 10

- -4

- 10

- -3

- 10

- -2

- 10

- -1

- 10

- 0

- C/I About Mean in dB

- Probability That C/I < Abscissa

**Before Combining**

**1 x 2**

**2 x 2**

**After Combining**

- Probability of C/I falling 15 dB below  mean is 300 times lower with 2 x 2 compared to  1 x 1

## Conclusion

- Achieving high capacity/coverage in a multi-cell BWA (50 speed & 50 QoS compared to mobile cellular) network is a challenging problem.
- Many technologies help improve performance. MIMO antennas are a key leverage.
- Gigabit Wireless is a pioneer of MIMO for BWA networks