ee359 – lecture 19 outline

EE359 – Lecture 19 Outline

AnnouncementsFinal Exam AnnouncementsHW 8 (last HW) due Thursday 5pm (no late

HWs)10 bonus points for course evaluations onlineProjects due Dec. 6 at 5pm

ISI/Inteference Rejection:Time-domain Analysis

Spreading Codes and Maximal Linear Codes

SynchronizationRAKE Receivers

Final Exam Announcements

Final 12/8/14 8:30am-11:30am in Thornton 102

Covers Chapters 9, 10, 12, 13.1-13.2 (+ earlier chps)

Similar format to MT, but longer: open book, notes.If you need a book or calculator, let us know

by 12/3/14

Practice finals posted (10 bonus points)Turn in for solns, by exam for bonus pts

Course summary and bonus lecture on advanced topics today, 4pm, here (pizza/cake/beer)

Final review, Sat Dec. 6, 4-5pm, followed by TA OHs, place TDB (check course calendar).

OHs this week Mine

Monday 12/1: 2:30-4pmTuesday 12/2: 10-11:30amSaturday 12/6: 2:30-4pm

TAs: Tues 12/2 : 4-6 pm, OHs+ disc,

Milind, 380-380YWed 12/3: 5-7 pm, OHs, Milind, Pack

109 Thursday 12/4: 1.30-2.30 pm,

Mainak, Pack 340Saturday 12/6: 4-6pm, Final Rev. +

OH, Mainak, location TBD (check course calendar)

Sunday 12/7: 2-3 pm, Milind, Pack 340

Review of Last Lecture:Design in OFDM, SS Intro

Design in OFDM: PAPR, time/freq offset, fading across subcarriers, MIMO-OFDM

Modulation that increases signal BW to combat narrowband interference and ISIAlso used as a multiple access

techniqueTwo types: Frequency Hopping

and DSSSFH: Hops info. signals over a wide

bandwidthDSSS: modulates info signal by chip

sequence

s(t) sc(t)

Tb=KTc Tc

S(f)Sc(f)

1/Tb 1/Tc

S(f)*Sc(f)

Review Cont’dISI and Interference

RejectionNarrowband Interference

Rejection (1/K)

Multipath Rejection (Autocorrelation ( ))r t

S(f) S(f)I(f)S(f)*Sc(f)

Info. Signal Receiver Input Despread Signal

I(f)*Sc(f)

S(f) aS(f)S(f)*Sc(f)[ad(t)+b(t-t)]

Info. Signal Receiver Input Despread Signal

brS’(f)

Today: We will derive the time-domain analysis for ISI and NB interference rejection

Maximal Linear Codes

Autocorrelation determines ISI rejectionIdeally equals delta function

Maximal Linear CodesNo DC componentLarge period (2n-1)TcLinear autocorrelationRecorrelates every periodShort code for acquisition, longer for

transmissionIn SS receiver, autocorrelation taken

over TbPoor cross correlation (bad for MAC)

1

-1 N Tc -Tc

Synchronization

Adjusts delay of sc(t-t) to hit peak value of autocorrelation.Typically synchronize to LOS

component

Complicated by noise, interference, and MP

Synchronization offset of Dt leads to signal attenuation by r(Dt)

1

-12n-1 Tc -Tc

Dt(r Dt)

RAKE Receiver Multibranch receiver

Branches synchronized to different MP components

These components can be coherently combinedUse SC, MRC, or EGC

x

x

sc(t)

sc(t-iTc)

xsc(t-NTc)

Demod

Demod

Demod

y(t)

DiversityCombiner

dk^

Main Points

DSSS rejects ISI by code autocorrelationMaximal linear codes have good

autocorrelation properties but poor cross correlation

Synchronization depends on autocorrelation properties of spreading code.

RAKE receivers combine energy of all MPUse same diversity combining techniques as

before