5G Mobile and Wireless Communication Systems for 2020 and Beyond
Ersin Öztürk February 2015
[email protected] Sayfa 1
The Wireless Roadmap •
In the past two decades, wireless communications has advanced greatly
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The simplest measure of performance increase has been advances in achieving higher data rates
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This trend for increased bandwidth has been following the exponential increase as shown in this figure
G. Fettweis, S. Alamouti, “5G – Personal Mobile Internet Beyond What Cellular Did to Telephony”, IEEE Commun. Mag., vol. 52, no. 2, pp. 97–105, Feb. 2014.
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Current Trends •
The thirst for data communications is going to continue and our transmission networks will most probably remain the bottleneck
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The landscape of information has expanded greatly to machines
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Machines will become an integral part of the global information network
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The nature of most of this data will be different than conventional human generated content, and will mostly be short, bursty, and asynchronous
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We need to build an efficient and smart architecture that can accommodate future demands for data communications
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The standards bodies and industry are now organizing a timeframe to standardize 5G technology
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Preliminary interest and discussions about a possible 5G standard have evolved into a fullfledged conversation that has captured the attention of researchers
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Current Trends (cont.) •
Preliminary research on the main features of future wireless networks has proposed capabilities that are substantially beyond those defined in the current 4G specifications
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Despite of its proven advantages, there are shortcomings that make it difficult for OFDM to address several of the 5G requirements
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There is a conceptual paradigm shift from synchronous and orthogonal to asynchronous and non-orthogonal systems
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We need increased robustness which will pose a number of research challenges
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In the center is the design of a new physical layer for 5G systems using nonorthogonal waveforms
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Novel concepts for multi-carrier communication are researched
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Schemes like Generalized Frequency Division Multiplexing (GFDM) and Filter Bank Multi-Carrier (FBMC) are considered in the research community
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All of these schemes can be classified as filter bank techniques and are related to the thoroughly investigated OFDM
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What drives 5G? •
The successful deployment of killer applications in wireless communication technology has allowed its rapid development in the past 20 years with major impact on modern life
Driver
Generation
Killer Application
1G
Untethered telephony
Wireless real-time voice communication
2G
Two-way paging
Text messaging (SMS)
3G
Widespread market adoption of laptop computers
Wireless data connectivity
4G
Shrinkage of the laptop, merging it with the cellular telephone into today’s smartphones • Cloud services • Connectivity of machines with other machines • Tactile internet
High rate wireless broadband access
5G
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• • •
Super high rate wireless broadband access, Internet of Things Real time cyber physical control 5
Key Scenarios for 5G •
New research projects have started internationally, and research centers devoted to 5G technology have begun to open
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There is a consensus between researchers for 5G scenarios, its technical objectives, key technologies and research areas
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There are three key scenarios for 5G •
Super-high rate low latency wireless broadband (Gigabit wireless connectivity)
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Internet of things (Machine Type Communications)
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Tactile Internet (real time cyber physical control)
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Key Technical Objectives for 5G 1. Data Volume (Aggregate data rate or area capacity) • 1000x higher mobile data volumes
2. End User Data Rate • Edge rate or 5% rate: From 100 Mbps to as much as 1 Gbps • Peak rate: Likely to be in the range of tens of Gbps
3. Number of Connected Devices • 10-100x higher
4. Latency • Current 4G roundtrip latencies are on the order of about 15 ms • 5G will need to be able to support a roundtrip latency of about 1 ms • A 1 ms round-trip time requires a time budget of max. 100 us on the physical layer
5. Energy and Cost • The per-link data rates being offered will be increasing by about 100×
• This means that the Joules per bit and cost per bit will need to fall by at least 100 • 10x longer battery life for low-power devices Sayfa 7
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Key Technologies for 5G 1.
Advanced Multicarrier Waveform • GFDM, FBMC, UFMC, BFDM
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Advanced Multiple Access • Non-Orthogonal Multiple Access (NOMA)
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Spatial Densification • More heterogeneous network deployments of macrocells, picocells, relays, and small cells
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Multiple RAT (Radio Access Technologies) support • 5G, 4G, 3G, Wi-Fi, device to device comm etc.
5. Spectral aggregation • Communicating on multiple frequencies simultaneously
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Milimeter Wave • Adopting new portions of spectrum such as the millimeter-wave bands
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Full Duplex Communication Sayfa 8 • Advanced interference cancellation/suppression
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Key Technologies for 5G (cont.) 8.
MIMO • Large antenna arrays or massive multiple-input multiple-output (MIMO)
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Backhaul aggregation • Backhaul connection from different cells into the core network
10. C-RAN • Base station processing is moved to the Internet cloud 11. SDN • Separation of data and control channels following the software defined networking (SDN) principles
12. NFV (Network Function Virtualization) • NFV enables network functions that were traditionally tied to hardware appliances to run on cloud computing infrastructure in a data center
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Key Technologies for 5G (cont.) 13. D2D (Device-to-Device) Communication • Device-centric network design instead of “cell-centric”and focus on the needs of user terminals 14. IOT • Machine-to-machine (IoT) communications support in an effective and integrated manner
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Physical Layer Evolution • The signaling and multiple access formats (the waveform design) have changed significantly at each cellular generation
• They have been each generation’s defining technical feature • 1G FDMA • 2G TDMA, CDMA
• 3G CDMA • 4G OFDM • 5G ????
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Multicarrier Modulation •
The explosion of mobile applications and data usage in the recent years necessitate the development of adaptive, flexible, and efficient radio access technologies
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Multicarrier techniques have been extensively used over the last decade for broadband wireless communications
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Multicarrier modulation is a method of transmitting data by splitting it into several components, and sending each of these components over separate carrier signals
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The individual carriers have narrow bandwidth, but the composite signal can have broad bandwidth
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Appealing Characteristics of Multicarrier Techniques:
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Support for multiuser diversity
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Simpler equalization
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Adaptive modulation and coding
Among many other multicarrier techniques, Orthogonal Frequency Division Multiplexing (OFDM) dominates the current broadband wireless communication systems Sayfa 12
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Advantages of OFDM •
Since each channel is almost flat fading, it is a natural way to cope with frequency selectivity and it only needs a one-tap equalizer to overcome channel effect
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It is a computationally efficient implementation via FFT/IFFT blocks
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Since OFDM allows for the spatial interference from multiantenna transmission to be dealt with at a subcarrier level, without the added complication of intersymbol interference, it is an excellent pairing for MIMO
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It has immunity to delay spread and multipath due to long symbol duration
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Since the subchannel is kept orthogonality with overlap it has efficient bandwidth usage with respect to classical FDM
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Drawbacks of OFDM •
The peak-to-average-power ratio (PAPR) is higher in OFDM than in other
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A high PAPR sets up an unattractive tradeoff between the linearity of the transmitted signal and the cost of the amplifier
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OFDM’s spectral efficiency is satisfactory, but could perhaps be further improved upon if the requirements of strict orthogonality were relaxed and if the cyclic prefixes (CPs) were smaller or discarded
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It is very sensitive to time and frequency synchronization
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It is very difficult to support short symbols with given channel delay spread
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OFDM is not robust under incomplete channel state information
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It has very high our of band emission
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Key Issues for the Physical Layer of 5G •
We want to allocate a pool of frequencies to users with relaxed or even no synchronization in time
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We want ultra-low latency physical layer in order to match with the human tactile sense
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We must implement sharp frequency notches and tight spectral masks in order not to interfere with other legacy systems
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Our waveform must be robust to asynchronous signalling and handle uncoordinated interference
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Do We Need a New Physical Layer for 5G? •
The transport mechanisms in LTE and LTE-Advanced have been tailored to maximize performance by enforcing strict synchronism and orthogonality
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Various emerging trends reveal major shortcomings of those design criteria: •
Machine-type-communications • Transmissions of this kind are suffering from the bulky procedures necessary to ensure strict synchronism
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Heterogeneous networks • Wireless networks are becoming more and more heterogeneous following the non-uniform distribution of users • Tremendous efforts must be spent to manage such systems under the premise of strict synchronism and orthogonality
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Fragmented spectrum • The introduction of carrier aggregation are forcing the transmission systems to deal with fragmented spectrum Sayfa 16
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Main Idea to Cope With Shortcomings of OFDM • Abandon synchronism and orthogonality altogether, thereby admitting some crosstalk or interference • To control these impairments by a suitable, most likely, more complex transceiver structure and transmission technique with a boost from advances in VLSI techniques
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Candidate Waveforms for 5G •
There are some explorative research proposals challenging the obedience of LTE and LTEAdvanced to strict synchronism and orthogonality with respect to the future applications
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They introduce non-orthogonal waveforms that carry the data on physical layer
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The four candidate waveform approaches are
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Generalized Frequency Division Multiplexing (GFDM)
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Filterbank-based Multi-Carrier (FBMC)
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Universal Filtered Multi-Carrier (UFMC)
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Bi-orthogonal Frequency Division Multiplexing (BFDM)
There are commonalities among those schemes, like including filtering, reduced spectral side-lobe levels and multi-carrier aspects, but also differences
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FBMC •
It is one of the most investigated filtered multicarrier systems
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The subcarriers are pulse shaped individually to reduce the OOB emissions
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It is typically used in conjunction with offset QAM
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Because the subcarriers have narrow bandwidth, the length of the transmit filter impulse response is usually long.
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Typically, the filter has four times the length of the symbols.
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FBMC can only achieve good spectral efficiency if the number of transmit symbols is large
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FBMC is not suitable for low latency scenarios, where high efficiency must be achieved with short burst transmissions
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Key open problems of FBMC are:
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Frame/frameless structure
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Synchronization
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Channel estimation (fragmented spectrum) and equalizations
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FBMC (cont.) • FBMC modulation can be considered as an evolved OFDM • Below transceiver structure is valid for both OFDM and FBMC • The difference between OFDM and FBMC lies in the choice of T and the transmitter and receiver prototype filters pT(t) and pR(t) (T is the symbol duration)
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GFDM •
The flexibility of GFDM allows it to cover CP-OFDM and single carrier frequency domain equalization (SC-FDE) as special cases
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It is based on the modulation of independent blocks, where each block consist of a number of subcarriers and subsymbols
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The subcarriers are filtered with a prototype filter that is circularly shifted in time and frequency domain
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This process reduces the OOB emissions, making fragmented spectrum and dynamic spectrum allocation feasible without severe interference in other users
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The subcarrier filtering can result in non-orthogonal subcarriers and both inter-symbol interference (ISI) and inter-carrier interference (ICI) might arise
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Nevertheless, efficient receiving techniques can eliminate this interference
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A matched filter receiver with iterative interference cancellation can achieve the same symbol error rate (SER) performance as OFDM over different channel models
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GFDM (cont.) •
It is a promising solution for the 5G PHY layer because its flexibility can address the different requirements
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GFDM is confined in a block structure of MK samples, where K subcarriers carry M subsymbols each
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So, it is possible to design the time frequency structure to match the time constraints of low latency applications
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The scheme retains all main benefits of OFDM at the cost of some additional implementation complexity
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All major synchronization algorithms developed for OFDM can be adapted for GFDM
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Space-time coding (STC) can be effectively combined with GFDM for achieving transmit and receive diversity
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Key open problems of GFDM are: •
Frame/Frameless structure
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Appropriate scheme for time and frequency synchronization
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Channel estimation
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GFDM (cont.) • GFDM falls into the category of filtered multicarrier systems • It offers more degrees of freedom than traditional OFDM or SC-FDE (Single Carrier-Frequency Domain Equalization) • GFDM turns into OFDM when M = 1, 𝐀 = 𝐅𝑁𝐻 and B = FN, (FN is a N × N Fourier matrix) • SC-FDE is obtained when K = 1 • SC-FDM (a FDM of several SC-FDE signals) is obtained when 𝑔 is a Dirichlet pulse
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UFMC •
It is a generalization of filtered OFDM and FBMC
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It uses a per-subcarrier-block-wise filtering and supports QAM
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Within blocks, orthogonality is provided, between blocks it is dropped
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High spectral efficiency can be reached in short burst transmissions
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It does not require a CP and it is possible to design the filters to obtain a total block length equivalent to the CP-OFDM
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Because there is no CP, UFMC is more sensitive to small time misalignment than CPOFDM
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UFMC might not be suitable for applications that require loose time synchronization to save energy
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Key open problems of UFMC are: •
UFMC is more sensitive to small time misalignment than CP-OFDM
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BFDM •
It employs well localized pulse shapes at the transmitter and receiver side that are biorthogonal to each other.
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The good frequency-localization of the transmit pulse makes the system robust against frequency dispersion (Doppler effect) while the good time-localization of the pulse provides robustness against time dispersion (multipath)
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Nevertheless, the Balian-Low theorem prohibits time-frequency well localized pulses when using standard QAM with maximum spectral efficiency
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Therefore, BFDM employs Offset QAM (OQAM) to achieve well localized pulses both in time and frequency domains
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It is especially efficient in the random access scenario
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Key open problems of BFDM are
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Critically dense BFDM cannot be easily integrated with MIMO aiming diversity, which is one of the key points for 5G applications.
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Similar to FBMC, BFDM needs to handle long pulse tails that reduces the efficiency for short burst transmission necessary in low latency and M2M applicationshas with very long symbol lengths
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Turkish SI Market Outlook
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