Outline 3G Evolution • High data rates: Fundamental constraints Chapter: 3 – High data rate in interference limited senarios – High data rates in noise limitted senarios • Higher data rates within a limited bandwidth : Higher order High data rates in mobile modulation communication – Higher order modulation in combination with channel coding Payam Amani • Variations in instantaneous transmit power Payam.Amani@eit.lth.se • Wider bandwidth including multi-carrier transmission Department of Electrical and Information Technology 3/19/2009 1 1 1 3/19/2009 3G Evolution - HSPA and LTE for Mobile Broadband 2 2 1 Rate control or power control [stefan Rate control [stefan Parkval] Parkval] 3/19/2009 3G Evolution - HSPA and LTE for Mobile Broadband 3 3/19/2009 3G Evolution - HSPA and LTE for Mobile Broadband 4 3
Higher data rates Higher data rates: Fundamental constraints • Shannon channel capacity: ⎛ + ⎞ S = ⋅ ⎜ ⎟ C BW log 2 1 ⎝ ⎠ N • Higher end user data rates compared to first 3G standards: one of the main targets for LTE – Channel only impared by ⎛ ⎞ ⋅ ⎛ + ⎞ S E R ⎜ ⎟ ≤ = ⋅ ⎜ ⎟ = ⋅ + additive white Gaussian noise b R C BW log 1 BW log 1 ⎜ ⎟ 2 2 ⋅ ⎝ ⎠ N ⎝ N BW ⎠ 0 • What do we mean by high data rates? R γ = BW – Main factors limiting the channel capacity: – Higher peak data rates E b γ ≤ + γ • Available signal power to log ( 1 ) – Higher data rates over the entire cell area 2 N noise power ratio 0 – Higher data rates on the cell edge ⎧ ⎫ • Bandwidth γ − E E 2 1 ≥ = ⎨ ⎬ b b min γ ⎩ ⎭ N N 0 0 3/19/2009 3G Evolution - HSPA and LTE for Mobile Broadband 5 3/19/2009 3G Evolution - HSPA and LTE for Mobile Broadband 6 Minimum required Eb/N0 at receiver as a Higher data rates: Fundamental constraints function of bandwidth utilization ⎛ + ⎞ S • Bandwidth utilization significantly smaller than one : = ⋅ ⎜ ⎟ C BW log 2 1 – Information rate cannot ⎝ ⎠ N exceed channel capacity. – Relatively constant minimum required Eb/N0 regardless of ⎛ ⋅ ⎞ ⎛ + ⎞ S E R bandwidth utilization. ⎜ ⎟ ≤ = ⋅ ⎜ ⎟ = ⋅ + R C BW log 1 BW log 1 b ⎜ ⎟ 2 2 ⋅ – Radio link bandwidth ⎝ ⎠ N ⎝ N BW ⎠ 0 γ utilization . R γ = • Bandwidth utilization larger than one (constant N0 and BW bandwidth): – Lower bound on the required E b received energy per γ ≤ + γ log ( 1 ) 2 information bit, normalized to N 0 – Eb/N0 increases rapidly by bandwidth utilization. the noise power density for a ⎧ ⎫ γ − – Increase in data rate: much larger increase in the minimum required E E 2 1 ≥ = given bandwidth utilization. ⎨ ⎬ b b min γ signal power at receiver. ⎩ ⎭ N N 0 0 3/19/2009 3G Evolution - HSPA and LTE for Mobile Broadband 7 3/19/2009 3G Evolution - HSPA and LTE for Mobile Broadband 8
High data rates in noise-limited Minimum required Eb/N0 at receiver as a function of bandwidth utilization senarios • When noise is the main source of radio-link impairment: Minimum required E b /N 0 at the receiver as a function of bandwidth utilization 25 – Increase of achievable data rates in a given bandwidth requires at least the same relative increase of signal power. 20 Power Limited Region Bandwidth Limited Region – Low bandwidth utilization: 15 Minimum required E b /N 0 (dB) • Power limited operation : increase in the available bandwidth does not 10 substantially impact what received signal power is required for a certain data rate. 5 – High bandwidth utilization 0 • Bandwidth limited operation : Furthere increase in data rate requires a much larger relative increase in the receive signal power unless the -5 -1 0 1 bandwidth is increased in proportion to the increase in the data rate. 10 10 10 Bandwidth Utilization γ 3/19/2009 March 19th, 2009 3G Evolution - HSPA and LTE for Mobile Broadband 3G Evolution - HSPA and LTE for Mobile Broadband 9 9 3/19/2009 3G Evolution - HSPA and LTE for Mobile Broadband 10 High data rates in noise-limited High data rates in noise-limited senarios senarios • To make use of the available SNR • How to increase overal received SIMO-MISO efficiently; transmission bandwidth signal power for a given transmit Proper combination should at least be the same order as signal power? the data rate to be provided. – Add antennas to the receiver side (Receiver antenna diversity)+ proper SIMO-MISO Proper combination combining • By reducing the range in theory we • Can increase the signal to noise can provide higher data rates. ratio after combining in proportion to the number of antennas. • Allows for larger data rates for the • Requiring bandwidth efficiency same cell range. greater or equal to one leads to – Add antennas to the transmitter Proper combination significant cell range reduction. (typically base station); focus a given total transmit power in the Proper combination direction of the receiver (beam • High data rates only available for forming). centre of the cell. • Can increase signal power and allow for higher data rates for the same MIMO cell range. 3/19/2009 3G Evolution - HSPA and LTE for Mobile Broadband 11 3/19/2009 3G Evolution - HSPA and LTE for Mobile Broadband 12
High data rates in noise-limited Receive diversity SIMO case senarios – SIMO and MISO efficiently provide SIMO-MISO higher data rates up to a certain • Addition of receiver antenna yields only a logarithmic increase in Proper combination level (saturation), i.e as long as the channel capasityin SIMO channels. Knowledge of channel information data rates are power limited rather than bandwidth limited. at the transmitter provides no capacity benefits. SIMO-MISO Proper combination – The mentioned saturation can be avoided by means of spatial ⎡ + ⎤ E multiplexing or MIMO. = 2 ⎢ s ⎥ C log 1 h 2 F ⎣ ⎦ N 0 SIMO – Details in chapter 6. 2 = = Proper combination h 1 , i 1 , 2 ,..., M i R – Alternatively one can reduce noise Proper combination power by designing a more advanced receiver with a smaller ⎡ + ⎡ + ⎤ ⎤ E E noise figure. = = ⎢ ⎢ s s ⎥ ⎥ C C log log 2 1 2 1 M M SIMO SIMO R R ⎣ ⎣ N N ⎦ ⎦ MIMO 0 0 3/19/2009 3G Evolution - HSPA and LTE for Mobile Broadband 13 3/19/2009 3G Evolution - HSPA and LTE for Mobile Broadband 14 Transmit diversity – MISO case MIMO system • In case of abcense of channel knowledge in transmitter there is no • MIMO system : benefit for MISO channels over SISO channels in sence of capacity. However in fading environment there is some benefits for MISO over • Channel has no prefered direction and is completely unknown to the SISO. If the channel is known to the transmitter the capacity is similar transmitter R ss = I MT . to the SIMO case. • Signals are independent and equi-powered at the transmit antennas. ⎡ + ⎡ + ⎡ + ⎤ ⎤ ⎤ E E E = = = 2 2 2 ⎢ ⎢ ⎢ s s s ⎥ ⎥ ⎥ Channel unknown to C C C log log log 2 1 2 1 2 1 h h h MISO MISO MISO MISO F F F ⎣ ⎣ ⎣ N N N M M M ⎦ ⎦ ⎦ E transmitter = + 0 0 0 T T T s y Hs n M T 2 = = if h 1 ( i 1 , 2 ,..., M ) i T ⎡ ⎤ E = + s H E C log 2 det ⎢ I HH ⎥ = + MIMO M s ⎣ ⎦ C log ( 1 ) R N M 0 T MISO 2 N 0 MIMO E ⎡ + ⎤ = + E C M log ( 1 s ) = 2 MIMO 2 Channel known to C log 2 1 ⎢ s h ⎥ Orthogonal channels N 0 MISO ⎣ F ⎦ N transmitter maximize capacity 0 2 = = = 2 = 2 M M M , H 1 , H M T R i , j F 3/19/2009 3G Evolution - HSPA and LTE for Mobile Broadband 15 3/19/2009 3G Evolution - HSPA and LTE for Mobile Broadband 16
Recommend
More recommend
