Transcript C30-20090330-047-DOrC - VIA.ppt

C30-20090330-047
DO Rev. C Proposal Update
Abstract: This contribution contains framework and components proposal update for DO R. C
Source:
Shu Wang
VIA Telecom
Contact: [email protected]
Recommendation:
Date:
review and adopt
30 March, 2008
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DO Rev. C Proposal Update
Shu Wang, [email protected]
VIA Telecom
Outline
HRPD Enhancements
 Subband OFDMA Multiuser Packet with C/I Sensitive DRC reporting
 MIMO OFDMA with Antenna Selection
VoIP Capacity Improvements
 Improve Delay-Limited Capacity with Frequency Diversity
 C/I sensitive DRC report for cell-edge ATs
 Subband hopping for high-C/I ATs
Cell Edge Performance Improvements
 Subband Interference Management.
 Dynamic frequency reuse.
 AN Macro Diversity.
 simple Broadcast Multicast Services
DO Rev. C Air Interface Roadmap: A VIA’s View
The adoption of multi-antenna techniques promises to improve
the performance of existing DO network infrastructure in a cost
efficient way.
 Improved link quality: spatial diversity and beamforming
 Higher Date rate: spatial multiplexing, multiuser MIMO
MIMO OFDMA with antenna selection provides a balance
between DO Rev. A/B and the full MIMO DO.
 OFDMA can also bring additional dimensions in optimizing DO
network when combined with multi-antenna techniques.
 It can improve the delay-limited capacity for VoIP-liked services
DO Rev. C with MIMO-OFDMA and antenna selection will be
more than a spatial extension of DO Rev A/B.
The additional layered transmission can help enable the simple
cooperation between ANs with minimum impact on the unicast
transmission of each AN.
Frequency Diversity (1/2): The Fundamentals
Full CQI Feedback
C/C0
No CQI Feedback
SNR (dB)
Source: D. Tse, P. Viswanath, Fundamentals of Wireless Communication
Frequency Diversity (2/2): Lessons We Learned
from Rev. B
Source: Airvana/CDG, EV-DO Rev. B white paper.
Using a single queue for N carriers in Rev B, as opposed to N independent
queues in Rev A, helps improve the user experience in the presence of
frequency-selective (frequency-dependent) fading.
This also is very important for VoIP liked applications, where the required
data rate for each user is not high but with strict low latency restriction.
Subband OFDMA (1/2): Strictly Backward
Compatible
Common Pilots
Layer-Modulated
OFDM
Layer-Modulated
OFDM
½ Slot, 1024 Chips
Common Pilots
MAC
Common Pilots
Pilot
MAC
Pilot
Layer-Modulated
OFDM
½ Slot, 1024 Chips
OFDMA Subband
OFDMA Subband
OFDMA Subband
OFDMA Subband
OFDMA Subband
OFDMA Subband
MAC
OFDMA Subband
Pilot
Common Pilots
MAC
Common Pilots
Pilot
Common Pilots
MAC
Power
Common Pilots
MAC
Power
Layer-Modulated
OFDM
MAC
Common Pilots
½ Slot, 1024 Chips
MAC
½ Slot, 1024 Chips
OFDMA Subband
OFDMA MUP puts the subpackets of multiple users into different subbands.
 Differentiate Tx power for the subbands for higher spectral efficiency.
 It provides additional support to the ATs on the cell-edge, in bad reception
condition or with delay sensitive services, and the single/dual antenna ATs.
Subband OFDMA is fully compatible with OFDM DO with additional features
 Adaptive DRC reporting:
 An AT reports DRCs for each subband only when the C/I is low and subband channel variation is
large. Otherwise, a single DRC is reported instead.
 An AT can feedback multiple DRCs for multiple subbands based on the MIMO operation mode.
 Adaptive OFDMA Preamble: Only the most efficient OFDMA preamble structure is used
by the AN, which depends on the employed OFDMA packing method.
Subband OFDMA (1/2): Frequency Reuse
OFDMA with Subband DRC Feedback,
especially for cell-edge ATs
OFDM
OFDM
OFDM
OFDM
•Strictly Backward Compatible with DO Rev. 0/A/B
•Seamlessly Compatible with Other OFDM DO Rev. C Proposals
Multi-ANTenna AT
It is non-trivial to “squeeze” more and more antennas
and RFs into a mobile phone with considering
 Power consumption.
 Mechanical limitation.
 Multiple radio interfaces there already: GPS, bluetooth, WiFi, …
 Antenna spacing requirement.
 For more spatial diversity gain, the separation should be larger than 0.5λ
 For 2GHz, the wavelength is about 15cm.
 Operating frequency bands.
MIMO with Antenna Selection is a most efficient way to
realize the potentials of multi-antenna techniques.
 There is little spatial diversity loss, as long as the multiplexing
gain is less than a certain threshold.
 The spatial multiplexing gain loss can be compensated through
frequency diversity.
Spatial Diversity Gain d(r)
(How reliable the link becomes )
Reliability/Throughput Tradeoff (1/2): The
Fundamentals
16
Full Antennas; N =4, L =N =4
Not much spatial diversity
gain loss, which happens
only when Lr is less than a
certain threshold
14
12
t
r
r
Full Antennas; N =4, L =N =2
t
r
r
Antenna Selection; N =4, L =2, N =4
t
r
r
Antenna Selection; N =4, L =3,N =4
t
r
r
10
8
The difference between
achievable spatial
multiplexing gains
6
4
2
0
0
1
2
3
Spatial Multiplexing Gain r
( How fast the achievable throughput increases )
4
Reliability/Throughput Tradeoff (2/2):
Implementations and Rank Deficiency
In theory, MIMO capacity is achievable with
 full-rank beamforming at the transmitter side
 successive interference cancellation at the receiver side.
There are tradeoffs between SCW and MCW MIMO.
 For a signal processing perspective, a SCW receiver is much
easier to be implemented.
In reality, rank deficiency reduces the achievable
throughput when
 there is strong correlation between Tx or Rx antennas OR
 the Rx antenna number is less than the Tx antenna number.
MIMO with OFDMA, frequency selectivity gain is added
to mitigate rank deficiency.
 A higher throughput is achievable even when rank deficiency
happens.
MIMO-OFDMA + Antenna Selection (1/2)
Rx antenna selection is a most cost efficient multiantenna technique to asymptotically achieve the full
potentials of MIMO techniques.
 It requires fewer RF chains, has less phone design limitation, lower
power consumption and lower manufacturing cost.
The achievable spectral efficiency can be close to those
with full RF chains with following techniques.
 Antenna Selection: the AT chooses some antennas for the next
Rx/Tx
 Beam Selection: the AT selects the best beams and feeds back the
PMIs.
 Subband Selection: the AT calculates PMIs for each subbands and
report back the best several PMIs to AN.
MIMO-OFDMA + Antenna Selection (2/2)
½ Slot, 1024 Chips
MIMO-OFDM
MIMO-OFDM
MAC
MIMO-OFDM
MAC
MIMO-OFDM
MAC
MIMO-OFDM
Pilot(s)
MIMO-OFDM
Pilot(s)
MIMO-OFDM
MAC
Subband
½ Slot, 1024 Chips
MIMO-OFDM
Each AT reports DRC for each subband, even in single-antenna or
SCW mode, for example.
 For each single-antenna AT, it reports DRC/PMI for each of the four
subbands.
 For each dual-antenna AT, it reports two DRC/PMI for each of two
subbands.
Four bits indicate the data rate request and 3 bits indicate the desired
serving sector. The channel has 64-ary bi-orthogonal modulation.
The DRC is sent on the Walsh codes W832 and W2432 and multiplexed
on the I and Q branches, which is similar to the DRC report in the
MCW mode.
Delay Sensitive Services
CDM DO was designed and optimized for high throughput.
 Multiuser diversity scheduling and slow power control with early termination.
However, delay-sensitive services may have different requirements on air
interface optimization.
 One key requirement is to minimize the delays for all served users. Then it is the
throughput or user capacity.
 As similar in 1x, the users in bad reception condition expect more Tx power while
the users in good reception condition may need less Tx power.
The achievable throughputs of delay-sensitive services are generally
optimized with delay-limited capacity instead of water-filling capacity.
 Multiuser diversity can still be the powerful tool improving the throughput.
The considerations for optimizing delay sensitive services include
 Channel Sensitive Scheduling in both Time and Frequency Domain
 Optimize the channel/user assignment for saving Tx power and minimizing interference.
 Dynamic Forward Power Allocation in Frequency Domain
 Reverse Power Control.
 The PC rate for the 1x is 800Hz with no early termination, 400Hz with early termination.
 Early Termination
 It works well with imperfect power control and more channel fluctuation.
Delay Limited Capacity and CQI Feedback
[The theory] For a single-user OFDM, the achievable delay-limited
capacity in low SNR region strongly depends on the delay spread,
not the path attenuations. In high SNR region, the roles are
exchanged.
From a multiuser scheduling perspective, one challenge is the
balance between maintaining fairness for weak-channel users and
maximizing throughput through strong-channel users.
 The full DRC feedback for weak-channel users can help the AN with the
efficient multiuser scheduling for delay sensitive services.
 For the ATs with good channel reception, a single CQI feedback with
necessary subband hopping is enough.
In addition, with full DRC feedback for cell-edge ATs, it can help the
AN not only schedule those ATs not only at a good balance between
throughputs and fairness but also the interference management.
C/I Sensitive DRC Reporting
DRC reporting is the mechanism to help AN with multiuser scheduling.
 Typically a 4-bit DRC value is bi-orthogonally coded.
DRC measurements can be obtained through both CDM time-domain
pilots and OFDM frequency-domain pilots
 The general C/I can be obtained from CDM pilots
 The frequency selectivity can be observed through frequency-domain pilots
DRC reporting can be optimized to reduce the feedback overhead for
OFDMA.
 Frequency selectivity gain is visible only when there is significant difference
between subchannel gains.
 When an AT sees the subchannel gains are pretty flat OR C/I ratios are pretty
high, it may just report one DRC for all subchannels.
 The packets for this AT will be transmitted with subband hopping or using all
subbands for frequency diversity.
 When an AT detects the variation of subbchannel gains is large AND C/I ratio is
not high, it may report multiple DRCs or the DRC for the best subband instead.
Subband Hopping
For the ATswith good C/I, subband DRC reporting is optional.
If a high-DRC AT feedbacks only a single DRC for all subbands,
AN has the following options
 Option 1: The packets for high DRC will generally be transmitted
through the whole 1.2288MHz bandwidth or all subbands.
 Option 2: The packets for high DRC can also be transmitted
through one subband or multiple subbands.
 The subband(s) allocated for the high DRC packet are not fixed. A
predefined subband hopping is applied.
If a high-DRC AT feedbacks multiple subband DRCs with
significant variation, the AN may schedule the AT in good
subband(s) with no subband hopping.
Cell-Edge Performance Improvements
CDMA2000 1x is well-known to be interference limited, especially
on cell edges: Pilot Interference, Overhead Channel Interference
and Traffic Channel Interference.
Multiple approaches are available for improving cell-edge
performance including
 Interference Management: power control and frequency reuse.
 Subband OFDMA Frequency Reuse and Interference Management
 Macro-diversity: cooperation between neighbor ANs.
 Simple Broadcast Multicast
Considerations for the AN Cooperation
 Soft combining has the advantage of simple receiver design and the
potential of 3 dB SNR gain.
 Soft combining puts more scheduling constraints on the ANs.
Interference Management with SFR
1
2
3
Subband
1.1
4
5
6
7
8
9
10
11
12
13
14
15
Time
OFDMA with Subband DRC Feedback,
especially for cell-edge ATs
the common suband shared by the sectors in cell 1
f1
Subband
1.2
Subband
2.1
Cell 1
Sectors
β
Sector Sector Sector
Sector Sector Sector
Sector Sector Sector
Sector Sector
Cell 1
Cell 1
Cell 1
1.α
1.β
1.γ
1.α
1.β
1.γ
1.α
1.β
1.γ
1.α
1.β
Sector
γ
Cell
1/2/3
Sectors Sectors
β
α
Sector
γ
Cell
1/2/3
Sectors Sectors
β
α
Sector
γ
Cell
1/2/3
Sectors Sectors
β
α
Sector
γ
Cell
1/2/3
OFDM
Stadium
f2
Subband
2.2
the common suband shared by all sectors
Park
Subband
3.1
Sector
Sector Sector Sector
Sector Sector Sector
Sector Sector Sector
Sector
Cell 3
Cell 3
Cell 3
Cell 3
3.γ
3.α
3.β
3.γ
3.α
3.β
3.γ
3.α
3.β
3.γ
3.α
Subband
3.2
the common suband shared by the sectors in cell 3
OFDM
OFDM
f1
OFDM
Shopping centre
Frequency
Interference management can be done in the subband level.
 Interference avoidance is achievable in time domain (slots), frequency
domain (subbands), space domain (sectors) and even through power
allocations.
 Finer granularity means higher achievable efficiency.
 It help mobile do handoffs with less ping-pong.
Subband frequency reuse can be done either through network planning
or the full CQI report from the cell-edge ATs.
Cell Cooperation with Broadcast and Multicast
Many emerging mobile services, e.g., alert service and positioning
assistance service, require the same FL multicast to cover multiple
sectors.
 It is similar to the full-fledged BCMCS but only for small-sized data
bursts, something like text message broadcast.
 Its coverage is expected to be more flexible. For example, a couple of
sectors or even one sector only.
FL multicast in UHDR-DO is for efficiently delivering the same content
to multiple users at the same time in one sector.
It is desired to extend the FL multicast to cover multiple sectors with
additional macro-diversity gains.
Mobile Radio
Access Network
Data Network
Assistance
Server
Assistance
Server
simple Broadcast Multicast Services
Physical Layer:
 More than one sectors can transmit the same signal streams
with the same content at the same time and frequency.
 For alleviating the scheduling constraints, the multicast
signal stream can be transmitted through MUP and layered
transmission.
 The pilots for separately the channel estimation of each layer are
superimposed together with special rotations
 One MUP MAC ID is especially reserved with multicast
capability.
MAC Layer: AT assigned an unicast MAC ID and multicast MAC
ID from each sector in its active set.
Connection Layer
 AN may assign Multicast MAC address via TCA
Pilots for Simple BCMCS
Frequency Domain Rotation
(Time Domain Delay)
Layer 1
Traffic
Channel
Coding
Channel
Interleaver
Repetition/
Truncation
Modulation
Gain
Control
Layer 2
Traffic
Channel
Coding
Channel
Interleaver
Repetition/
Truncation
Modulation
Gain
Control
MUX
Pilots
Scramblers
For the soft combining simple BCMCS data from different sectors, the
sector-specific overheads transmission are separated from the data
transmission.
The data can be transmitted from a separated layer, which has a layerspecific pilots.