Smart Antenna And Mc-Scdma

C802.20-03/29

Smart Antenna and MC-SCDMA
Next Generation Technologies for Wireless Broadband

Guanghan Xu, CTO Navini Networks

August 16, 2011

April, 12 2001

1

C802.20-03/29

Outline
•

Comparative Analysis of CDMA, OFDM, and MC-SCDMA

• Comparative Analysis of Smart Antennas vs Conventional Antennas • Comparative Analysis of TDD vs. FDD • Optimal Integration ofTechnologies to Create a Broadband Solution • Field Trial Results of the Integrated Technologies

C802.20-03/29

Wireless Broadband Challenges
Path Loss (Link Budget)
14.4Kbps to 1Mbps = 69 times or 18dB more power

Multipath Fading

Intercell Interference
F1
F1 F1 F1

F1
F1

Suburban

t
Free space

F1
F1 F1

Time Domain

City

Rural

Mixture of Broadband & Narrowband(voice)
f
Frequency Domain

0.1

1

2

3 5

10 20 km

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OFDM Multiple Access
• OFDM offers very good immunity to multipath issues. • FFT is very efficient in channelization NlogN instead of O(N2). • OFDM needs much higher fade margin requiring higher signal levels and complex coding. • OFDM has high peak to average ratio that impacts link budget due to large PA backoff. •OFDMA is difficult to reliably transmitting narrowband data or voice due to the spectrum nulls. Frequency hopping does smooth out the probability of hitting the nulls. • OFDM is susceptive to intercell interference in the N=1 deployment while all the neighboring cells are fully loaded.
Transmitted OFDM Spectrum

f

Received OFDM Spectrum

Signal Threshold

f

C802.20-03/29Conventional CDMA
+ + +
Transmitted CDMA Spectrum
Received CDMA Spectrum
Interference Signal

f

f

Frequency Domain

Frequency Domain

Code 1 Code 2 Code 3

Code 4

• CDMA (1XEVDO, EVDV & WCDMA) all have asynchronous CDMA uplink.
• Due to high spreading gain, CDMA (1X and WCDMA) signals are more resistant to intercell interference which enables N=1 deployment. • Since each code hassufficient bandwidth, signal fading is marginal. • Due to high intercode or intracell interference, the link budget is adversely impacted leading to the cell breathing effect. • The high intracell interference also considerably reduces the capacity or throughput of the system.

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Synchronous CDMA (SCDMA)
Symbol Period

+ + +

Code 1

Code 2

Code 3

Code 4

•Synchronous CDMA (SCDMA) can maintain code orthogonality and its

multipath interference or intercode interference is minimized. • Due to the spreading gain, the SCDMA signals are also more resistant to intercell interference which enables N=1 deployment. • Since each code has sufficient bandwidth, signal fading is marginal.

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Multipath Effect to SCDMA
Multipath Channel of User 1

++ + + +
Multipath Channel of User 2

+ + + +
Symbol Period
Other User Interference Self Interference User 1 Signal User 2 Signal Code 1 Code 2 Code 3 Code 4

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Joint Detection for SCDMA
• Joint detection is the solution to effectively handle the multipath in multiuser CDMA systems. • Joint detection is computationally expensive and its complexity is O(N2L), where N is thespreading factor and L is the channel length. • Increasing N leads to more resistence to signal fading and the ability to assign lower data rates to handle the mixture of narrowband and broad applications

• Increase N does increase the complexity of joint detection quadratically.
• Wide bandwidth (1.2288Mcps for IS-95 or 1X, 3.84Mbps for WCDMA) also leads to small chip periods or relativelyincreases L which will increase the complexity and degrade the performance.

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Optimal Tradeoff: MC-SCDMA

f

f

WCDMA
Best on signal fading Worst on multipath interference Good on intercell interference

f

OFDM
Best on multipath interference Bad on intercell interference Worst on signal fading
f

f

MC-SCDMA
Optimal tradeoff among multipath interference,...