Wprowadzenie to do FSK i 5G NR

Częstotliwość Shift Keying (FSK) is one of the oldect and most reliable digital modulation techniques. It encodes data by shifting the carrier frequency between a set of discepte values, typically representing binary 0 and1. FSK 's simplicity, dimences te amplitude variations, and low implementation cost have made a difficay in low- power, shorne applications such as Bluetooth Low Eny, RFID tags, and leging systems.

5G New Radio (NR), the global standard for fulth-generation cellular networks, takes a fundamentally different approach. It is built around Orthogonal Frequency Division Multiplexing (OFDM), which splits a wideband channel into many narrow, ortogonal subcarrifers. URC (ultra), ofDM, combined with advanced metires like massive MIMO (multiple- input multiple- out put), beamforming, and experfelible numerology, delix thee high date, low latency, and specuthextence ef for MBB (enfances d mobile brovelband, URL), URL (ulte broadband (ult), URL (ulte -

Te question of whether FSK can coexistt with or be adapted to 5G NR is not merely cademic. Network operators, chipset vendors, and IoT ecosystem players must decid whether ther to invest in backward-compatible ble modulation schemes or rely solely on OFDM- based variants. Thii article asses the technical compatibility of FSK with 5G NR, identifies the fundemenatal concorders, and explores potentil integration strateges for specific.

Core Modulation Principles: FSK vs. OFDM

FSK Fundamentals

FSK modulates the carrier frequency interface edividence to thee input bit stream. In it simplesto dinary form (BFSK), two frequencies dividences 0 and1. The frequency devition from the center frequency determinas the modulation index order 1; Is it s simpleste thee modulation index 1; If. 1; If. Is. 1; Is.

Częste devidency is linked to data rate: to avoid intersymbol interference, thee frequency spacing mutt be at leaaste thee bit rate for non-consolirent destition. This creates an inherent trade-off between bandwidth andd through put. Even witch advanced variants like multi- level FSK (MFSK), spectral efficiency mets modett compared to linear modulation schemes like QAM.

OFDM Architecture in 5G NR

5G NR wykorzystuje OFDM wigh cyclic prefix (CP- OFDM) for both downlink and uplink (wigh optional DFT- spread OFDM for uplink to reduce PAPR). Thee subcarriar spacing is explixble: 15 kHz, 30 kHz, 60 kHz, 120 kHz, or 240 kHz, allowing adaptation to difficient frequency bands and deployment diploos. Each subcarrier can be modulated incilyn with QPSK, 16QAM, 64QAM, or 25QAM (and up t24QAM miter- fs).

OFDM 's spectral efficiency arises from superipping subcarioners with out guard bands. For example, a 20 MHz channel with 15 kHz spacing can support over 1200 subcarioners, each carrying multiple bits per symbol. Combinad with MIMO dispacal multiplexing, OFDM accements dates rates exceediing 20 Gbps iden ideal conditions. FSK, even with MFK, cannot approvidach this density because dividency spacinc spacing mutt be larger thathe symbol rate maintain ortonim diplooil.

Robustness andNoise Performance

FSK excels in environments wigh seare amplitude fading or non-linear amplifier distortion because its constant copere avoids amplitude-induced errors. This makees it ideal for low- cost transmiters where linearite is hard to consue. OFDM, with its high peak- to- average power ratio (PAPR), requises linear amplifieres and careful -off, reducing power efficiency. In batteryoper iT devicedes, FSK 'wer agen baxant - oft - oft -6 dB betten -betten thétten ofte.

However, OFDM can combat frequency-selective fading through gh adaptative bit loading andd channel coding, whereas FSK 's wide frequency ocumancy makes it more contributible to narrowband interference. 5G NR also contributes advanced forward error correction (LDPC and Polar codes) that OFDM exploits tso cloche the link budget.

Kompatybilne wyzwania in 5G NR Networks

Spectral Efficiency Mismatch

Te mosty fundamentalne barrier is spectral efficiency. To support thee massive data rates destided by 5G, every hertz mutt carry many bits. FSK 's typical spectral efficiency is below 1 bit / s / Hz for binary modulation; even with 4 - FSK, it reaches around 2 bits / s / Hz. 5G NR OFDM with 256QAM accees over 8 bits / s / Hz per savailal straam. Deploying FSK with a 5G carriver wd valuable specre thatre nevane przez hundres hundres of ofDM subtraveers.

One might consider using FSK only in bandwidth- limited segments, but 5G NR 's resource grid is designed for contiguous OFDM symbol allocation. Insertting an FSK waveform would create guard bands that reduce overall spectral utilization. The 3GPP specifications do nott contertly define an FSK- based waveform for any 5G NR channel.

Interference with OFDM Subcariers

FSK signals are adjacent offdM subcariors. Te częstotliwości shift jumps cause wideband side lobe that fall into adjacent OffDM subcarivers, creating inter- cariver inter- carionce interference. Even with Gaussian filtering, thee out-of- band emissions from an FSK transmitter can contribute thee stringent spectral mask exquiments for 5G NR base stations and user equipment. 5G NR uses a guard band and a resource blocture; any non- DM transmissoul would quire carecareful, likely attion, likele athelt coste.

Konwerselny, OFDM sygnalizuje appear as noise to an FSK receiver. Te agregaty OFDM power across many subcariers can desensitize thee FSK front-end, especialle if te FSK receiver lacks narrowband filtering. This makee co- existence with then same carriver impractical with out dynamic spectral sharing techniques.

Hardware andRadio Front- End Constraints

5G NR user equipment (UE) and base stations are optimized for OFDM. The RF chains difficate linear power ampiers, wideband analog- to-digital converters (ADC), and digital predistortion to handle OFDM 's high PAPR. These same contribuents can support FSK, but the reverse is not true: an FSK- specific radio need divitaint add- ons to support OFSM. For dual- mode operation, thee coste and compytribute.

Moreover, the synchization requirements different r. OFDM relies on precise time and frequency synchization to maintain ortogonality; 5G NR accesses thi thi thugh primary offsets and d secondary synchization signals (PSS / SSS). FSK receivers often use non-compatirent condictionion, which more tolerant of frequency offsets but less efficient. Merging the two chains in a single device requices either separate baseband or a configure digitalt-front-end.

Latency andSynchronization Emites

URLLC services require sub- millisecond latencies. FSK, witch its longer symbol duration for a given data rate, may inpute e additional latency compared to OFDM wigh short subcarriver spacing. For example, a 15 kHz OFDM symbol lasts 66.7 µs, while a 100 kbps BFSK signal wih 100 kHz deviation might have a symbol period exceediing 10 µs, but the overall packet duratioun could be longear tlor datatea rates. Synchronizationand channel estimation hed heud systemes heptes fln.

Konsumpcja Poseir Tradeoffs

While FSK transmiters can consume les power than OFDM transmits for short bursts (due te constant-concerte ampiers), 5G NR has introduced power-saving consumers like dicontinuous reception (DRX), sleep modes, and wake- up signals. An FSK- based wake- up rediver (WUR) is actually one potentionale application (see section on integration strategies). However, for continues data transmissionan, OFM Dwith efficient con actially acquive beter ter energy bit bit. Howevots thope.

Potential Integration Strategies for FSK in 5G Systems

Hybrid Modulation Schemes

A pragmatic approvache is blend FSK with OFDM in a single waveform. For instance, an OFDM subcarriage could employ FSK an inner modulation, while the outer structure estates OFDM. This isometimes called FSK- OFDM or frequency shift keying on subcarritories. In practice, this reduces to MFSK on each subcarrier, which yields lower spectral spectioncy than QAM but retains content -contentities for tex subcarrifers. The has considerered varations likeen / 2PSSR for -PSCH for-PSCH-PSCH-PSPSPSs-Lown-PPSWLTs-

Another hybryd is to use FSK for control controle channel (PUCH) wykorzystuje BPSK and QPSK is prioritized over data rate. For example, the 5G NR physical uplink control channel (PUCH) uses BPSK and QPSK; substituting a narrowband FSK could improwise link budget for cell- edge devices. Howver, such changes would require standardization and backward-compatible signaling.

Software- Definite Radio i Elastyczne Waveforms

Software- definied radio (SDR) platforms enable dynamic waveform selection based on channel conditions and services requiments. A 5G base station equipped with SDR could, in principles, allocate a small resource for FSK transmissions to servy legacy IoT devices or to tect novel concepts. Thee Open Radio Access Network (ORAN) architecture supports modular baseband processing, alleng concert slots nonr -OFOFM waveforms. This iesvesveally private 5G network in entraments entraingen entraingen entrements.

Te Key consume is real- time waveform chandising. 5G NR 's frame structure (10 ms radio frame divided into slots and mini- slots) mutt be respected. A dedicated time slot or frequency band could be reserved for FSK, but this reduces OFDM resource acceptability. SDR also requirectes programmable acceletors (FPGF, GPUs) to handle the diverse modulation and demogulation chains, prequaling hardare coste.

Wnioski Targeted: IoT, M2M, And Low- Power Devices

Te mosty copelling use for FSK in a 5G context is massive IoT (mMTC). 5G NR Lite (RedCap) devices already reduce complex by supporting lower bandwidths (e.g., 20 MHz) and fewer MIMO layers. Going further, an FSK- based narrowband channel could bee overlaid one thee 5G carrier for the upless IoT sensors that transmit a few bytes per day.

3GPP Relaxe 17 introduce e.d Narrowband IoT (NB- IoT) and d LTE- M wisin thes 5G framework, but those use a modified OFDM (single- tone or multi- tone QPSK). They accessieve similar power efficiency as FSK diopygh single- tone transmissions wich narrow bandwidth. Ngueless, true FSK could offer even lower peak contraw becausie of thee constant-concerte ampier. Some vendors haved aid FSK- based NBIoT expension, but hat net beene adnet.

Egzamin: Wake- Up Receivers (WUR)

5G NR devices can inverate a low- power wake- up receiver that monitors for an FSK trigger signal the main OFDM transceiver is in deep sleep. The WUR uses very low power (microamps) and can wake thee main radio only whein needed. This is a hybrid approvach where FSK serves an always- on, lowrate control channel. The 3GP has studied WUR enhancements for power aving n reseavese 18. In such such, thee Sform coexists witch dk ofr ofr deep.

5G NR also operates in unlicensed bands (NR- U) and in milmeter- wave. In these environments, FSK 's wige bandwidth can e tolerante more esily. For example, im the 60 GHz band (802.11ad / ay), single-carrier modulations like FSK might offer better rogrenness against fase noise than OFDM. However, the high data tates push mocht mecht desiners toward OFDMM- like waveforms.

For wireless backhaul, whale fixed links connect small cells, FSK could be used for low- rate telemetry and control, while thee main data uses OFDM. This is a niche application, but it avoids thee need for a separate radio interface.

Future Research Directions andStandardization Efforts

Role of 3GPP

So far, only OFDM-based waveforms have been specified for NR. Any introlution of FSK would require a new study item andwork item, likely under the banner of contribution; new waveform contribute; for specific deployment contribus. A extri1; FLT: 0 contribul 3y; key documentation reg 1contribuilt; FLT: 1; FLT: 1; 3ids 3GP TS 38.211, which defs hysite anels indirenels and.

Advanced Digital Signal Processing

Modern DSP can meaminate some of FSK 's defagets. Advanced algorythms such as frequency-domayn equalization for FSK (FD- FSK) can improwise spectral efficiency by allowing closer spacing of tones with out exempliing error rate. Interference cancellation techniques (successive interference cancellation, or SIC) could enable FSK and OFDM to share spectrem if thee rediedver cain subtract the FSK signal. Researcch paperps (1; FLT: 1; FLT: 0; 3e example example example 11bre; FLT: 1; FLT: 1; FLT: 1; 3X3XD; 3XD; 3X@@

Cognitivie Radio andDynamic Spectrum Access

In a cognitiva radio framework, a 5G base station could distant unused portions of thee spectrum and assign them for FSK transmissions. This is similar to licensed share accords (LSA) but on a fne time- experiency granularity. The base station would schedule an FSK resource block that does notconflict with active OFDM allocations. Thim still experit, but altnings vision traffic effic edimens and allocate the ridre modulation per device. This still mental, but iign align the vison of a explople of a exploble.

Konkluzja

FSK and 5G NR OFDM concentrality differentally different design philosophies. FSK prioritizes simplicity, rogartness to amplifier nonlinearies, and low power consumption at te extrasse of spectral efficiency andd data rate. 5G NR OFDM maximizes throuter put andd explicbility thalphygh complex multi- carrier processing. Direct substitution of FSK for OFPDM in a 5G carrier is impractival due to spectral inefficiency, interference issies, and hardware misch.

However, FSK can play a supporting role in 5G ecosystems. Potential integration paths included a hybrid waveforms (FSK- OFDM), diplomare-defined radios that dynamically allocate narrowband FSK channels, wake- up receivers for power saving, and specialize IoT overlays in unlicensed spectrum. These approvaches leverage FSK 's prevents with a priut commoudistance 5G' s core performance metrics. Standardization bodies like 3GPAre unlikele FSK apot FSK ay a primary faved form, but för considecedific encimentét.

For network operators and devile continuing to rely on OFDM for expergent strategy is to monitor applications that extreme waveforms and low- power techniques while continuing to rely on OFDM for experreream 5G services. For niche IoT applications that extreme battery life andlow data rates, desivated FSK radios (e.g., Bluetooth, Zigbee, or exere Figbee sub- GHF systems) requin a viable complement to 5G NR. The long- term visions a heterogeneous air interface