1. Channel Bonding versus Channel Aggregation
July 2006
doc.: IEEE yy/xxxxr0
July 2006
Channel Bonding versus Channel Aggregation
IEEE P Wireless RANs Date:
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Carlos Cordeiro, Philips
Carlos Cordeiro, Philips

2. July 2006
Introduction
The purpose of this presentation is to compare the Channel Bonding and Channel Aggregation techniques with respect to the following evaluation criteria:
FRD satisfyability
Increased bandwidth
Impact on RF
Impact on PHY
Impact on MAC
Practical Issues
In this presentation we show that for contiguous channels, channel bonding is the best technical solution
Channel aggregation cannot (does not make sense to) operate over adjacent channels
Carlos Cordeiro, Philips

3. Outline Background Review of FRD Increased Bandwidth
July 2006
Outline
Background
Review of FRD
Increased Bandwidth
Theoretical Capacity
Simulation Results
Channel Bonding vs Channel Aggregation
An RF Perspective
A PHY Perspective
A MAC Perspective
Practical Issues
Carlos Cordeiro, Philips

4. Background Channel bonding is for contiguous channels only
July 2006
Background
Channel bonding is for contiguous channels only
Thus, for a fair comparison between channel bonding and channel aggregation, only contiguous channels shall be considered
Throughout this presentation, the following scenario, referred to here as the Comparison Scenario, is used:
Carlos Cordeiro, Philips

5. July 2006
Review of FRD
“The typical range of the system is 33 km (based on 4 Watt CPE EIRP and 50% location availability at the edge of the coverage area for a median location and 99.9% time availability F(50, 99.9))”
“The required minimum peak throughput rate at edge of coverage SHALL be 1.5 Mbit/s per subscriber in the forward direction and 384 kbit/s per subscriber in the return direction”
Carlos Cordeiro, Philips

6. Increased Bandwidth: Capacity Increase
July 2006
Increased Bandwidth: Capacity Increase
Bonded TV channels to get more capacity
Shannon: C = B.log2(1+S/N)
Capacity proportional to BW, but logarithmic with SNR or signal power
If S/N is fixed, then capacity increases linearly with bandwidth.
If signal power is fixed, but bandwidth is increased
C = B.log2(1+S/(BNo))
Capacity still increases as bandwidth is increased
Carlos Cordeiro, Philips

7. Increased Bandwidth: Capacity Increase
July 2006
Increased Bandwidth: Capacity Increase
Capacity of bonded channels as a given signal power is spread over more channels
Carlos Cordeiro, Philips

8. Increased Bandwidth: Simulation Scenario
July 2006
Increased Bandwidth: Simulation Scenario
6 MHz System:
2048-FFT
32 users, each with 64 carriers, all assumed to be data. Distributed subchannelization and interleaving over 6 MHz.
Cyclic Prefix Length: 512 samples
12 MHz System
4096-FFT
32 users, each with 128 carriers, all assumed to be data. Distributed subchannelization and interleaving over 12 MHz.
Cyclic Prefix Length: 1024 samples
Channel: Exponentially faded Raleigh channel with 7 ms rms delay spread (total delay spread: 70 ms).
Both systems have same multipath protection, and will be compared based on same data-rate.
Carlos Cordeiro, Philips

9. Increased Bandwidth: Performance Improvement
July 2006
Increased Bandwidth: Performance Improvement
About 5 – 6 dB
gain with channel-bonding
over two channels, with
same total transmit power.
Carlos Cordeiro, Philips

10. Channel Bonding vs. Channel Aggregation: An RF Perspective
July 2006
Channel Bonding vs. Channel Aggregation: An RF Perspective
In case of channel aggregation
Given the lack of appropriate isolation, the transmission through channel X may cause RF problems in channels X-1 and X+1
When channel X is transmitting, channels X-1 and X+1 cannot receive, and vice-versa
Synchronized is needed – major problem!
Such very tight synchronization is likely impossible in practice
Randomness in traffic, real-time, beyond the scope of IEEE 802 (above MAC)
Major incumbent protection issue: if channel aggregation is done at CPEs, it can violate incumbent protection (more info later)
These issues are not encountered when channel bonding is used
Carlos Cordeiro, Philips

11. Channel Bonding vs. Channel Aggregation: A PHY Perspective
July 2006
Channel Bonding vs. Channel Aggregation: A PHY Perspective
When using channel bonding, the guard band in between channels (Guard BandA) can be reused
On the other hand, a larger guard band is required at the band edges (Guard BandB)
Once the OFDMA parameters are finalized in the spec, we can define Guard BandA and Guard BandB
This will lead to extra capacity (about 10%) for channel bonding over aggregation
Carlos Cordeiro, Philips

12. Channel Bonding vs. Channel Aggregation: A MAC Perspective
July 2006
Channel Bonding vs. Channel Aggregation: A MAC Perspective
Facts:
Channel bonding incurs no additional overhead as all control messages are transmitted only once
Superframe header consumes only 4-5 symbols over a 160ms period
With channel aggregation, the overhead increases considerably with the number of channels used
For an effective channel aggregation solution, features such as sophisticated scheduling, load balancing, channel management, etc., are needed
High cost and complexity
With channel bonding, the BS and CPE have much greater control and freedom on resource allocation, transmit power, etc.
Implementation is much simplified
From the MAC perspective, channel bonding is a much superior technical solution
Carlos Cordeiro, Philips

13. Channel Bonding vs. Channel Aggregation: A MAC Perspective
July 2006
doc.: IEEE yy/xxxxr0
July 2006
Channel Bonding vs. Channel Aggregation: A MAC Perspective
The MAC can simultaneously support single channel and multi-channel CPEs
Capacity as needed (up to subscriber)
Product differentiation
Controllable by BS, etc.
Alert-Window (AW)
Contention slots for initial ranging
Used by AAS CPEs and by single channel CPEs
Carlos Cordeiro, Philips
Carlos Cordeiro, Philips

14. Channel Bonding vs. Channel Aggregation: A MAC Perspective
July 2006
Channel Bonding vs. Channel Aggregation: A MAC Perspective
The MAC functionality to support channel bonding and aggregation have been implemented in OPNET
Some simulation parameters
Superframe size = 16 frames, where Frame size = 10 ms
Packet size = 1 Kbyte
64-QAM rate 2/3 and Symbol time = 310 µs
Carlos Cordeiro, Philips

15. Simulation Experience
July 2006
Simulation Experience
Basic aggregation
While no change is required to the scheduler for channel bonding support, the added complexity to the code to support aggregation was substantial
Attempt to implement tight Allocation Start Time (AST) control over channel aggregation
Attempted to use LaGrange multipliers. Could not do it.
Spent a few days looking at other techniques. Could not do it.
Problem
if you have asynchronous traffic only you can hardcode AST, but the wastage of resources is significant
If you have isochronous traffic, you simply cannot do it without sacrificing QoS
Conclusion: Unless we see a way to do it, we cannot support this idea. As far as we know, it is undoable.
Carlos Cordeiro, Philips

16. Channel Bonding vs. Channel Aggregation: A MAC Perspective
July 2006
Channel Bonding vs. Channel Aggregation: A MAC Perspective
Evaluate the performance at the MAC SAP under varying number of TV channels
1 BS and 127 CPEs
Carlos Cordeiro, Philips

17. Channel Bonding vs. Channel Aggregation: A MAC Perspective
July 2006
Channel Bonding vs. Channel Aggregation: A MAC Perspective
Aggregation incurs much more overhead than channel bonding
Aggregation and bonding are designed for medium-high loads, and in these cases bonding clearly surpasses aggregation
Even though the throughput is the same, the overhead is much larger with aggregation
Carlos Cordeiro, Philips

18. Channel Bonding vs. Channel Aggregation: A MAC Perspective
July 2006
Channel Bonding vs. Channel Aggregation: A MAC Perspective
Evaluate the protocol efficiency of aggregation and bonding
Protocol Efficiency = (Data bits Rx/Total bits Tx)
The MAC protocol efficiency with channel bonding outperforms that with channel aggregation
A consequence of the much lower additional overhead of bonding
Carlos Cordeiro, Philips

19. Channel Bonding vs. Channel Aggregation: A MAC Perspective
July 2006
Channel Bonding vs. Channel Aggregation: A MAC Perspective
Evaluate the channel utilization
Bonding can offer much better channel utilization, with less overhead
Carlos Cordeiro, Philips

20. July 2006
Practical Issues
Far out CPEs may not be able to be serviced by a BS employing aggregation, but may be serviced by one using channel bonding
A single customer cannot have more than one CPE in his/her premises, otherwise it will cause harmful interference to nearby TV receivers (as per the 10m separation assumption)
Therefore, channel aggregation is not possible at the CPE level (even though, in practice, nothing can be done by IEEE to avoid it)
Channel bonding is the only way to offer higher capacity or range at the CPE level
Note: Nowhere in the FRD is stated that physical location of CPEs have to be known by the BS. This cannot be presumed.
Channel bonding is a more cost effective than channel aggregation
Does not require additional radios
Channel bonding is much less complex than channel aggregation
Does not requires a number of other complex features (e.g., load balancing, sophisticated scheduler, etc.) that are needed with aggregation
Carlos Cordeiro, Philips

21. July 2006
Conclusions
For contiguous channels, bonding is a much more technically sound approach
Channel aggregation is not feasible for contiguous channels
Channel bonding also allows for product differentiation
We have shown that when considering the FRD, bandwidth, and the impact on RF, PHY, and MAC, channel bonding is the option of choice for contiguous channels
Carlos Cordeiro, Philips