Unlicensed Spectrum

• The unlicensed spectrum has enabled many low-cost wireless services from medical monitors to walkie-talkie and Wi-Fi.

• The 2.4 GHz band is currently the most utilized band shared by different wireless users such as cordless phone, ZigBee, Bluetooth and Wi-Fi .

• with 2.4 GHz band, 5 GHz band is less congested and mainly used by Wi-Fi(11a) devices.

• The unlicensed 60GHz band has more abundant bandwidth ,making it feasible for bandwidth-intensive multimedia services [7]. However, the severeoxygen absorption and atmospheric attenuation at 60 GHz band imposes great challenges in the design of physical layer specifications and air interfaces

The 5GHz frequency band

This band is frequently referred as 5GHz UNII (Unlicensed National Information Infrastructure) band, having 3 sub-bands (1,2 & 3)

Most Regulatory Areas offer a large amount of spectrum in the 5 GHz band In Europe there is 455 MHz of spectrum available, and 580MHz in the US The use of unlicensed spectrum usually carries some regulatory requirements, such as being

able to detect if a radar system is using the band or being able to co-exist with other users of the band

In some regulatory areas, like Europe and Japan, there is a specific requirement for supporting LBT (Listen-Before-Talk) or Clear Channel Assessment (CCA) at milliseconds scale is required

In other regulatory areas, like US, Korea and China, there are no such requirements Other techniques are also needed like DFS (Dynamic Frequency Selection) in UNII-2 sub-band

for optimizing the co-existence between different systems or technologies

Band AIndoor only30-200mW

5150 (200MHz) 5350 Band C

Outdoor1W

(125MHz) 5850 Band B

Outdoor1W

5470 (255MHz) 5725

The 5GHz frequency band

LTE-U• originally developed by Qualcomm, using

the 4G LTE radio communications technology in unlicensed spectrum, such as the 5 GHz band used by dual-band Wi-Fi equipment.

• LTE-U was first introduced in Rel13 of the 3GPP standards, LTE-U is built upon the carrier aggregation capability of LTE-Advanced.

Design PrinciplesSome fundamental principles and regulations are imposed to guarantee the harmonious coexistence between LTE-U and other incumbent systems

•The transmission power•Listen Before Talk and Dynamic frequency selection •Licensed Assisted Access•Carrier aggregation

The transmission power• The first issue in the use of unlicensed spectrum is the regulation of transmission

power. Such regulation is specified to manage the interference among unlicensed users.

• indoor wireless access points (APs) in business buildings, which often falls within the 5.15 − 5.35 GHz spectrum band, the maximum transmission power is 23 dBm in Europe or 24 dBm in US.

• outdoor, e.g. hotspot picocell, allows a maximum of 30 dBm which usually happens within the 5.47 − 5.85 GHz spectrum band. Besides the maximum transmission power, the 5.25 − 5.35 GHz and 5.47 − 5.725 GHz spectrum has mandated (TPC) mechanisms. • transmit power control (TPC) reduces the power of a radio transmitter to the

minimum necessary, in order to avoid interference to other users and/or extend the battery life while maintaining the link transmission quality.

Dynamic frequency selection (DFS)

Meteorological radar systems also operate on the 5 GHz unlicensed spectrum, thus the unlicensed devices may drop non-negligible interference upon the normal radar .

LTE-U devices periodically detect whether there are radar signals and will switchthe operating channel to one that is not interfering with the radar systems upon detection.

Mechanism named dynamic frequency selection (DFS) is adopted in 5.25−5.35 GHz and 5.47−5.725 GHzspectrum.

Listen-before-talk (LBT) and Dynamic frequency selection (DFS)

Listen-before-talk (LBT) and Dynamic frequency selection (DFC)

listen-before-talk (LBT) mechanism Any device wishing to use the band must listen to see if it is occupied.

If the band isn’t busy, the device can seize it and start transmitting. The band can only be held for a maximum of 10 milliseconds after which it must be released and the LBT process repeated.

Licensed-Assisted AccessLicensed-Assisted Access operation

• Aggregation of a primary cell, operating in licensed spectrum to deliver critical information and guaranteed Quality of Service, with a secondary cell, operating in unlicensed spectrum to opportunistically boost data rate

• The secondary cell operating in unlicensed spectrum can be configured either as downlink-only cell or contain both uplink and downlink

Licensed-Assisted Access• In the downlink, prior to downlink data transmission, the eNB will sense the channel. If

available, the eNB schedules a user for data transmission based on the proportional fair scheduling metric. Under the current carrier aggregation framework, cross-carrierscheduling may be used as shown in Fig. 2 or the scheduling grant may be sent on the SCell as well.

• In the uplink (when the unlicensed channel is used for both downlink and uplink), however, the eNB must schedule data transmission k subframes ahead of time (e.g., k=4 for FDD). In this case, the eNB does not know whether the channel will be free and thus it will be up to the UE to sense the channel before beginning data transmission in the assigned subframe. If the channel is not free, the UE will refrain from transmission. The eNB can then reschedule this transmission using either the primary or secondary carrier.

Licensed-Assisted Access• LAA as supplemental downlink will be evaluated. This is usually the more

interesting case as typically the downlink data traffic is significantly larger thanthe uplink data traffic. A simple CCA mechanism is used to detect the energy level during sensing. If the energy level is below a threshold (i.e., the channel is deemed to be clear), the eNB is allowed to transmit. Otherwise the eNB continues sensing until the channel is clear, and then selects a randomback off amount in number of sub frames up to a maximum of 2 sub frames. The eNB will commence data transmission only after the channel is clear for the specified duration.

Carrier aggregation

• Carrier aggregation (CA)increase the overall bandwidth available to a user equipment by enabling it to use more than one channel, either in the same band, or within another band.

• Carrier Aggregation can be applied to both Frequency Division Duplex (FDD) and Time Division Duplex (TDD) variants of LTE and it allows the combination of different carrier bandwidths in number of ways.

Carrier aggregationIn (a), is where the carriers are contiguous and lie within the same frequency band. In this case it is feasible for a mobile device to handle the signals using a single transceiver, providing it is able to operate efficiently over the aggregate bandwidth.

In (b) shows intra-band non-contiguous carrier aggregation, in which the carriers lie within the same frequency band, but they are not adjacent. In this case it is necessary for the mobile device to use a separate transceiver for each carrier

In (c) show inter-band non-contiguous carrier aggregation ,In this case the carriers fall in different parts of the radio spectrum, such as 900MHz and 1800MHz.

Investigations and Scope in LTE-U 1.LTE uses scheduled transmission, how can LTE scheduled transmission work with LTB (Mitigations Techniques)? ,will regulators enforce good neighbor on WI-FI not spoil the coordination /good neighbor policy done via LTE?

In some country like US, Korea, China, the answer is Yes, you (a cell) can use the allowed spectrum at anytime as long as it would not create serious Co-existance problem. But in some countries like EU and Japan, the answer is NO. The cell should perform a specific process called LBT (Listen Before Talk) .

1.LTE uses scheduled transmission, how can LTE scheduled transmission work with LTB (Mitigations Techniques)? will regulators enforce good neighbor on WI-FI not spoil the coordination /good neighbor policy done via LTE?

LTE-U the cell use another mechanism called CSAT (Carrier-Sensing Adaptive Transmission). Technically, CSAT is very similar to CSMA, the main difference is that CSAT monitors(senses) the medium for much longer duration (around 10 s of msec to 200 msec) comparing to normal WiFi CSMA, so that it would not infere not only with WiFi data transmission (QoS traffic) but also with more sporadic transmission like discovery signals.

why LTE-U is such a friendly neighbor to Wi-Fi. LTE-U does not use all of the available 5 GHz band, over 200 MHz is exclusively available for Wi-Fi. LTE-U is a downlink-only technology, meaning LTE-U end devices will not generate any interference to Wi-Fi or any other technologies in the 5GHz band. An LTE-U small cell scans portions of 5 GHz looking for a vacant channel, and if there is no vacant channel, it finds the least occupied channel. It then takes turns using that channel with Wi-Fi users, ensuring that it never uses the channel more.

1.LTE uses scheduled transmission, how can LTE scheduled transmission work with LTB ? will regulators enforce good neighbor on WI-FI not spoil the coordination /good neighbor policy done via LTE?

The requirements DFS to detect radio stations DFS-enabled radios monitor the operating frequency for radar signals. If radar signals are detected on the channel, the wireless device takes these steps. If the wireless device does not select a DFS-required channel, it enables beacons and accepts client associations.If the wireless device selects a DFS-required channel, it scans the new channel for radar signals for 60 seconds. If there are no radar signals on the new channel, the wireless device enables beacons and accepts client associations. If a radar signal is detected, the wireless device selects a different channel. If a preferred channel is configurable and available, it is selected first. When a DFS–enabled radio is operating on one of the following channels, the wireless device uses DFS to monitor the operating frequency and switch to another frequency or reduce power as necessary.

1.1Mechanisms for scheduling LTE-U and Wi-Fi

Within different access classes for Wi-Fi, each Wi-Fi station gets equal opportunity to access airtime. We right said the pre-standard proposals for LTE-U operate much differently. Those scenarios use a duty cycle approach, which means the LTE-U operator determines if there’s Wi-Fi operating in the channel LTE-U intends to use, makes an assessment of the environment, and then decides what percentage of the airtime should be allocated for Wi-Fi and for LTE operations is [non contention base] , then all are scheduled but in Wi-Fi are probabilistic based on random back off.

2.How is actually the ecosystem of the LTE on unlicensed spectrum ?,In order to of the radio access providers , and how is the internetworking with LTE on licensed spectrum ?

The ecosystem for unlicensed wireless is vast .It involves regulatory authority operators , equipment vendors , consumer products and millions of users .Equipment technology in unlicensed bands is varied :Wi-Fi , Bluetooth ,Zigbee .These technologies and devices have sources .Their basic principle is" Live and let Live ."If they see interference , they backoff .If they see someone else using the resources , they wait for their turn.

Their question is whether LTE-U will cooperate and compete?

With CSAT, LTE-U will ensure that resources are shared fairly. This way, Wi-Fi access points in the area will not be starved just because LTE-U is also operating in the same area. LTE-U has the ability to intelligently switch off transmission so that resources are released for Wi-Fi.

We can say the ecosystem of LTE technology is mature enough .

3.The difference btw Unlicensed be both TDD and FDD in the coverage ?

FDD deployments provide greater coverage than TDD Mobile devices in a Frequency Division Duplexing (FDD) system transmit on a continuous basis, which enables devices to achieve cell edge rates farther from the base station. Mobile devices in a Time Division Duplexing (TDD) system transmit periodically (e.g., 1/2 or 1/3 of the time compared to FDD); hence, required rates cannot be achieved at similar distances when compared to FDD. The FDD advantage is consistent regardless of the radio technology being used.

4.At 5GHz high frequency range –what range /distance could the typical LTE-U small cell support ? Will be similar to/better than WI-FI for similar output power levels ?• LTE-U stands for "LTE unlicensed," because it's LTE that works on the unlicensed 5 GHz spectrum, now occupied by Wi-Fi

routers. This has also caused much controversy, because eventually carriers could crowd out Wi-Fi routers with LTE-U "routers" or cells.

5.Hypotheticall,if every carrier in a region (say USA) uses the unlicensed spectrum for LTE would not this spectrum support too many subscribers and bog down (similar to the challenge of WI-FI in a crowded space where everyone gets signal but no one can use WI-FI? ? Why do not aggregate the Wi-Fi technology directly ?

• But proponents of LTE-U insist that the technology has spectrum-sensing capability that can identify open frequencies not occupied by other unlicensed users. They also say that LTE-U has "adaptive duty cycle" that allows it to take turns with other user.

• Its important to mention that the CSAT (carrier sensing adaptive transmission )cycle, ON/OFF period will be dynamically configurable based on traffic and other performance metrics. Second, LTE-U will perform channel selection based on energy detection. There will be a hierarchical system which channel LTE-U will occupy.

5.Hypotheticall,if every carrier in a region (say USA) uses the unlicensed spectrum for LTE would not this spectrum support too many subscribers and bog down (similar to the challenge of WI-FI in a crowded space where everyone gets signal but no one can use WI-FI? Why do not aggregate the Wi-Fi technology directly ?

Wi-Fi1.PHY is half-duplex

2.PHY is packet oriented – sync on each packet

3.PHY provides a single channel with a single modulation for each packet

4.Access is by CSMA/CA , Probabilistic - based on random back offe:Networks function without frequency planning

5. Stochastic interference

6. The access points coordinate together.

LTE-U1.PHY is typically full-duplex2.PHY operates continuously – sync is interspersed3.PHY provides multiple channels simultaneously with varying modulation

4.All client access is scheduled5.Adjacent networks require frequency planning

5.Deterministic Interference .

6. They can do not coordinate each other together and they have backhaul property btw the cells .

Better spectrum efficiency than the current technologies in use with the 5 GHz band. Since LTE radio technology is based on state of the art technology, it can achieve both high data rates and at the same time high spectral efficiency, also in the unlicensed band. As well as higher capacity, LTE technology offers better coverage, especially when combined with the use of licensed band operation.

The use of both licensed and unlicensed spectrum offers end users higher data rates and overall better performance when the unlicensed band operation is available. The use of carrier aggregation means the licensed spectrum can quickly take over to ensure service quality should the unlicensed spectrum become unusable for any reason, such as reduced coverage, interference from another system or avoidance of, for example, a radar operating in the band.

Based on the studies conducted, the LTE technology can meet the regulatory requirements for the unlicensed band and allow coexistence with the other LTE systems as well as other technologies, such as Wi-Fi, operating on the same frequency band.

Benefits of LTE-U

Reference • Backhauling

• The backhauling is the part of the network with the highest capillarity, covering the entire territory. Typically deployed with a three or hub and spoke topology, with direct connectivity between sites and no alternative traffic path. It requires high reliability products, capable of high flexibility in deployment and scalability in capacity.

Equipment in this case need both full IP as well as hybrid configuration support. Need to be compact in size and easy to install and commission. Although split mount represent the vast majority of instalments, full outdoor solution are constantly growing adding a new level of flexibility.

• Aggrgation

• Pre Aggregation and Aggregation network collects al the traffic from the backhaul. This part of the network runs high capacity traffic, and relies on networking technologies to ensure traffic protection. At this point of the network interworking and awareness of fibre technologies become fundamental to optimize the behaviour and the performances of the network to satisfy the QoS needs.

• https://www.siaemic.com/index.php/applications/fixed-mobile-convergence/backhauling-and-aggregation