Page 85 - ITU Journal Future and evolving technologies Volume 2 (2021), Issue 4 – AI and machine learning solutions in 5G and future networks

ITU Journal on Future and Evolving Technologies, Volume 2 (2021), Issue 4

Fig. 1 shows a snapshot of the 5 GHz band in Wi‑Fi (partic‑ • Probabilistic Uniform (PU): as an alternative to
ularly, U‑NII‑1 and U‑NII‑2 bands are shown), where ba‑ SCB and AM, PU is introduced to add some random‑
sic 20 MHz channels can be bonded to form wider chan‑ ness in the process of picking free channels, so that
nels of up to 160 MHz. Each allowed channel is repre‑ any combination is chosen with the same probabil‑
sented by an identi ier. For instance, channel 36 is the ity. This policy has been shown to improve both SCB
irst 20 MHz channel in the U‑NII‑1 band. As can be ap‑ and AM in some scenarios in which low starvation
preciated, the number of combinations for bonding chan‑ was present due to inter‑BSS interactions.
nels is high, even for a small portion of the available
1
spectrum and under the constraint that only contigu‑ To better illustrate the behavior of CB policies, Fig. 3
ous channels can be bonded. Moreover, novel bonding shows a simpli ication of the transmission procedure that
techniques combine Orthogonal Frequency Multiple Ac‑ a Station (STA) follows when implementing AM. In par‑
cess (OFDMA) with preamble puncturing [9] to use non‑ ticular, CB may be applied over channels 1‑4. Based on
contiguous channels. With all this, given the number of the AM policy, at time , the STA can transmit only over
1
Basic Service Sets (BSSs) and devices in crowded deploy‑ channel 2, which is the only one that is sensed free at
ments (see Fig. 2), we can say that CB is a problem with a the moment of initiating a transmission. Similarly, in ,
2
combinatorial action space. both channels 1 and 2 are found free, so the transmission
is performed over those two channels. Finally, provided
that the entire spectrum is free, a transmission over chan‑
nels 1‑4 is performed at . Notice that, if applying SCB,
3
the STA would have not been able to transmit until . Al‑
3
ternatively, regarding PU, any combination of free chan‑
nels could have been selected in and .
3
2
Ch 1
Ch 2
Ch 3
STA
Ch 4
t 1 t 2 t 3

Channel busy
STA's transmission

Fig. 3 – Dynamic channel selection for transmitting when applying DCB.
Fig. 2 – Dense WLAN deployment with multiple CB con igurations. Each
number in the list of channels represents one basic 20 MHz channel.
Through the analysis conducted in [8], it was shown that
the right channel choice is not always trivial (i.e., selecting
2.2 Policies for dynamic channel bonding
the widest channel does not necessarily entail achieving
To harness the available spectrum within the CB opera‑ the highest performance). First of all, using wider chan‑
tion, Dynamic CB (DCB) mechanisms [7, 8] are applied to nels entails spreading the same transmit power over the
decide the set of channels for transmitting on a per‑packet selected channel width, which can potentially affect the
basis, thus potentially improving performance. In [8], the data rate used for the transmission, and therefore the ca‑
following DCB policies were proposed and analyzed: pabilities of the receiver on decoding data successfully.
Moreover, the potential gains of DCB in crowded deploy‑
• Static Channel Bonding (SCB): a transmitter is al‑ ments are hindered by the interactions between Wi‑Fi de‑
lowed to use the entire set of channels only, thereby vices, which may provoke contention or collisions. The
limiting the election of any subset of channels. While
fact is that WLAN deployments are unplanned and op‑
such a policy may optimize the performance in iso‑ erate under Carrier Sense Multiple Access (CSMA). From
lated deployments, it lacks the necessary lexibility the perspective of a given transmitter‑receiver pair, such
to deal with inter‑BSS interference.
a lack of coordination leads to uncontrolled interference
• Always‑Max (AM): in this case, the widest combina‑ that can potentially degrade their performance.
tion of channels is picked upon having sensed them
free during the back‑off procedure. While such a Other DCB mechanisms were proposed in [10, 11, 12, 13],
which include collision‑detection, carrier sensing adap‑
policy seems to properly harness the available spec-
tation, or traf ic load awareness. More recently, ML and
trum, it has also been shown to generate starvation
game theory have been applied to address CB as an
and other issues as a result of inter-BSS interactions.
online decision-making problem involving multiple
1 In the 5 GHz and 6 GHz bands, there are six and fourteen non‑ agents [14, 15].
overlapping channels of 80 MHz, respectively.

© International Telecommunication Union, 2021 69