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  • 1. Telecom TutorialsMonday, June 03, 2013www.tempustelcosys.comIntroduction to Radio Link Control forReal Frequency Hopping Networks
  • 2. Monday, June 03, 2013www.tempustelcosys.comRadio Link Control Options:Frequency Hopping, Power Control and DTXReal network simulation environmentSimulation resultsCapacity gains vs. re-useHomogeneous vs. real network layoutsDifferent hopping modesRecommendations with respect to operator’s bandwidthConclusions
  • 3. Monday, June 03, 2013www.tempustelcosys.comPower Control (PC)Discontinuous Transmission (DTX)Frequency Hopping (FH)Interference increase by tighter frequency re-usecan be compensated for by combination of FH, PC and DTXreduces interference due to minimum transmission powerreduces interference due to no transmission during silence periodsmitigates frequency selective Rayleigh fading for slow MSsaverages interference due to interference diversity Tight frequency re-use yields capacity gain in existing sites at moderate costHow far shall re-use be tightened for optimum performance?Planned re-use down to 4 ? Cluster 1x3 ? Cluster 1x1
  • 4. Monday, June 03, 2013www.tempustelcosys.comFH, PC and DTX are mandatory (for MS) GSM Phase 1 featuresFH: GSM 05.02PC, DTX: GSM 05.05 and 05.08PC dynamic range MS (GSM 05.05):GSM 900 phase1: 39 dBm (33 dBm typ.) - 13 dBm 8 W (2 W typ.) - 20 mWGSM 900 phase2: 39 dBm (33 dBm typ.) - 5 dBm 8 W (2 W typ.) - 3 mWGSM 1800/1900: 36 dBm (30 dBm typ.) - 0 dBm 4 W (1 W typ.) - 1 mWPC dynamic range BS (GSM 05.05):TRX Power class (GSM 900: 320 .. 2.5 W, GSM 900 Micro 250 mW .. 25 mW)Static RF power step: 0 .. -12dB (2dB steps)Dynamic RF power control: 0 .. -30 dB (2dB steps)
  • 5. The information of one GSM speech frame is spread over8 successive burstsMonday, June 03, 2013www.tempustelcosys.com20 ms speech frameTDMA frame0 1 2 3 4 5 6 7channel coding & interleavingIsolated corrupted bursts can be compensated by a strong forward error correctionby convolutional channel codingSoft decoding exploits mix of “good” and “bad” bursts
  • 6. Due to multi-path fading, the radiochannel is frequency selectiveChanging the transmission frequencyfrom burst to burst leads to individualpropagation conditions for each burstMonday, June 03, 2013www.tempustelcosys.com|H(f)| [dB]ARFCN0-10-20-30n n+1 n+2 n+3 n+4 ...
  • 7. Monday, June 03, 2013www.tempustelcosys.comTDMA framen n+1 n+2 n+6n+3 n+4 n+5 n+725 7751 103SACCH period: 480 msSpeech Frame period: 20 msTDMA frameWavelength: 900MHz ~ 30 cm, 1800MHz ~ 15 cmMS movement within one Speech Frame vs. SACCH period3.6 km/h (1 m/s) 50 km/h (~14 m/s)TCH/FS 20ms 2 cm << 28 cm ~SACCH 480ms 48 cm > 670 cm >>TCH/FS performance strongly depends on FH at low speedSACCH perf. (radio link timeout!) fairly independent of FH
  • 8.  Frequency diversity gains are limited by the number ofrepetitions of frequencies within the interleaving depth,e.g. 8 for TCH/FSCyclic FH reaches max. gain of e.g. 5 dB at 8frequenciesRandom FH reaches max. gain of e.g. 5 dB at 64frequenciesMonday, June 03, 2013www.tempustelcosys.com
  • 9.  In the non-hopping case, on all bursts the sameinterferer occurs, i.e. no interference diversityMonday, June 03, 2013www.tempustelcosys.comInterfering Cell TRX 11 1 1 1 1 1Interfering Cell TRX 22 2 2 2 2 2Interfering Cell TRX 33 3 3 3 3 3Reference Cell TRX 11 1 1 1 1 1TDMA frame # n n+1 n+2 n+3 n+4 n+5Interfering Cell TRX 44 4 4 4 4 4TDMA frame # m m+1 m+2 m+3 m+4 m+5
  • 10. Even in the cyclic FH, on all bursts the same interferer occurs, i.e. nointerference diversityMonday, June 03, 2013www.tempustelcosys.comReference Cell TRX 11 2 3 4 1 2Interfering Cell TRX 13 4 1 2 3 4Interfering Cell TRX 24 1 2 3 4 1Interfering Cell TRX 31 2 3 4 1 2Interfering Cell TRX 42 3 4 1 2 3TDMA frame # n n+1 n+2 n+3 n+4 n+5TDMA frame # m m+1 m+2 m+3 m+4 m+5
  • 11. In the random FH case, from burst to burst different interferers occurrandomly, i.e. interference diversityMonday, June 03, 2013www.tempustelcosys.comReference Cell TRX 13 1 3 2 2 4Interfering Cell TRX 13 2 4 4 1 4Interfering Cell TRX 24 3 1 1 2 1Interfering Cell TRX 31 4 2 2 3 2Interfering Cell TRX 42 1 3 3 4 3TDMA frame # n n+1 n+2 n+3 n+4 n+5TDMA frame # m m+1 m+2 m+3 m+4 m+5
  • 12.  With FH:  C/I decreases, raw BER and RXQUAL get worse But:  Voice quality (FER) improves Simulations can evaluate FH gainsMonday, June 03, 2013www.tempustelcosys.comFER [%]probability 2% FERC/I [dB]per locationprobabilityCyclic FHRandom FHno FH10%
  • 13. Monday, June 03, 2013www.tempustelcosys.comIdeal homogeneous celllayout• homogeneous propagationconditions• homogeneous trafficdistribution etc.real world effects areneglectedReal inhomogeneous cell layout• various propagation conditions,depending on site position,topology, morphology,antennae ...• inhomogeneous trafficdistributionreal world effects are taken
  • 14. Monday, June 03, 2013www.tempustelcosys.comRadio Network Planning (Tornado)• network configuration• pathloss predictions• frequency planReal Network System Level SimulatorRadio Network Model• Cell selection• MS positioning• implementation of FH,PC, DTX andGSM multi-frame structure• calculation of CIRburstCIRburstStatistical Radio Link Model• mapping of CIRburst ontoBER, FER, 1bRBER• quality metrics, e.g. FER• planning guidelines• parameter settings
  • 15. Capacity is limited by the minimum ofhard blocking, e.g. fulfilling Erlang-B Table at 2% (red dashed line)soft blocking, e.g. fulfilling quality criterion FER 2% for 90% of the callsMonday, June 03, 2013www.tempustelcosys.com02040608010012014021 14 9.3 7 4 1x3 1x1Erl/Sitemean TCH re-use, opt. assignment clusterReal Network2/2/23/3/34/4/45/5/5Co-Channel InterferenceCo- and Adj. Interference02040608010012014021 14 9.3 7 4 1x3 1x1Erl/Sitemean TCH re-use, opt. assignment clusterIdeal Homogeneous Network2/2/23/3/34/4/45/5/5Co-Channel InterferenceCo- and Adj. InterferenceOperator Bandwidth: 8.6 MHz, i.e. 43 channels (15 BCCHs + 28 TCHs)FH, PC and DTX used
  • 16. Monday, June 03, 2013www.tempustelcosys.comReal networks have sites off grid, varying propagation conditions etc.Cluster 1x3 may lead to large areas which actually use re-use 1 resulting inpoor voice quality and handover problemsCluster 1x3 cannot address omni-sitesMean Re-Use 4 Cluster 1x3
  • 17. Monday, June 03, 2013www.tempustelcosys.com5 hopping frequencies,re-use 7 (frequency planning)27 hopping frequencies,re-use 1x1CH profits from better frequencydiversityInterference diversity from individualfreq. sets per cell01020304050607080Erl/SitePC DTX PC & DTXRHCHFH only01020304050607080Erl/SitePC DTX PC & DTXFH only
  • 18. Monday, June 03, 2013www.tempustelcosys.com
  • 19. Monday, June 03, 2013www.tempustelcosys.com
  • 20. Monday, June 03, 2013www.tempustelcosys.comReal Network, Co- and Adj. Interference02040608010012014021 14 9.3 7 4 1x3 1x1Log-NormalFadingErl/Sitemean TCH re-use, optimum assignment cluster2/2/23/3/34/4/45/5/5= 3dB= 5dB= 7dBAbsolute Erl/Site values significantly depend on simulation assumptions likesigma of log normal fading,QoS requirements etc.Relative comparisons of optimum assignments vs. cluster 1x3 and 1x1 holdirrespective of log normal fading
  • 21. Monday, June 03, 2013www.tempustelcosys.com024681012146 12 18 24 30 36 TCH freq.Erl/Site/MHz= 7 dB024681012146 12 18 24 30 36 TCH freq.Erl/Site/MHz= 5 dBLimited spectrum: reuse 1x1 recommendeddue to higher FH gainsSufficient spectrum: planned reuse (e.g. 6) recommendeddue to better C/I and sufficient FH gainsPlanned re-use profits more on measures to achieve homogeneous network design
  • 22. Monday, June 03, 2013www.tempustelcosys.comSignificant capacity gains can be achievedby FH, PC and DTX in dedicated TCH andBCCH bandsCapacity and quality are determined bya trade-off betweenlocal mean C/I in the networkFH interference diversity gainsTwo distinct ways can be chosen to maximise capacity:re-use 4 in random FH for good C/I and good interferencediversityre-use 1x1 with MAIO management in random FH for maximuminterference diversityRe-use 1x3 ignores 4 colour theorem leading to poor C/I andinsufficient FH gains in real networks (“bad compromise”)Depending on operator spectrum, re-use 1x1 is recommended forlimited spectrum and re-use 4 or higher for sufficient spectrum