Differential Impacts of Doppler Shift on LEO Satellite IoT Communications in Different Frequency Bands

מרץ 12 2026

Frequency band selection is a core part in the design of LEO satellite IoT systems. Different communication bands differ significantly in frequency range, propagation characteristics and spectrum resources. Since the magnitude of Doppler shift is directly related to the signal transmission frequency, the impacts of Doppler shift on different bands show obvious differentiated characteristics. Meanwhile, different bands impose distinct requirements on Doppler compensation techniques, which directly determine the technical design difficulty and hardware implementation cost of the system. This paper focuses on analyzing the Doppler shift characteristics and impacts of L-band and Ka-band, comparing the differences with other major bands, and explaining the divergent requirements of frequency band selection on Doppler compensation techniques, so as to provide a reference for frequency band selection in LEO satellite IoT.

Differential Impacts of Doppler Shift on LEO Satellite IoT Communications in Different Frequency Bands

I. Doppler Shift Characteristics and Impacts of L-Band

L-band (1.5–1.6 GHz) is an important traditional frequency band for LEO satellite IoT communications. Its downlink frequency range is 1525–1559 MHz and uplink 1626.5–1660.5 MHz, with a total bandwidth of 34 MHz. Combined with its frequency and propagation properties, the influence of Doppler shift in this band is characterized by small magnitude and easy compensation. However, constrained by spectrum resources, its application expansion is somewhat limited.

(1) Core Doppler Shift Characteristics

The most prominent feature of L-band is its relatively small Doppler shift magnitude. Due to the low carrier frequency, the absolute frequency shift caused by the same satellite velocity is much lower than that in high-frequency bands. Taking an LEO satellite at 600 km altitude as an example, the Doppler shift in S-band (2 GHz) is about 48 kHz, while that in L-band is approximately 38 kHz, a reduction of about 20%. The small shift magnitude greatly lowers the requirement for frequency offset compensation capability of receivers, and traditional compensation techniques are sufficient for system demands.

Meanwhile, L-band has excellent propagation performance with strong diffraction and penetration ability, and is less affected by weather. It can maintain good communication quality in dense building areas and severe weather conditions. Such propagation characteristics can compensate for the performance loss caused by Doppler shift to a certain extent and improve system communication stability.

In addition, as a traditional band for satellite mobile communications, L-band spectrum has been almost fully occupied by existing systems, making it difficult to obtain new frequency resources for satellite-terrestrial integrated communication. The scarcity of spectrum resources limits the capacity expansion of L-band systems, requiring technological innovation to improve spectrum efficiency for large-scale IoT connections.

(2) Impacts in Practical Applications

In LEO satellite IoT scenarios such as short-message communication, continuous data transmission and positioning applications, the impacts of Doppler shift vary:

For short-message communication, the cumulative effect of Doppler shift is limited due to small data volume and short transmission time, and simple frequency offset compensation can meet communication requirements.
In continuous data transmission, the persistent influence of Doppler shift demands more sophisticated frequency offset tracking algorithms such as pilot-based estimation and adaptive compensation to ensure transmission stability.
In positioning applications, L-band provides relatively high Doppler shift measurement accuracy, and its low shift rate helps improve positioning solution accuracy, making it one of the preferred bands for LEO satellite positioning.

II. Doppler Shift Characteristics and Impacts of Ka-Band

Ka-band (26.5–40 GHz) is a core band choice for high-rate LEO satellite IoT communications. With advantages of large bandwidth and high data rate, it is critical for high-rate applications such as high-definition data and large-file transmission. However, its high carrier frequency leads to extremely severe Doppler shift challenges with large magnitude and fast variation, imposing extremely high requirements on system design.

(1) Core Doppler Shift Characteristics

Ka-band Doppler shift features two core properties: extremely large magnitude and fast variation rate. According to 3GPP technical reports, LEO satellite links in Ka-band may experience Doppler shift up to ±480 kHz to ±600 kHz. Taking a transmission frequency of 25.995 GHz as an example, the Doppler shift at 780 km orbital altitude can reach 726.9 kHz, far higher than that in medium and low bands. Meanwhile, the Doppler shift rate of Ka-band systems can reach 0.27 ppm/s, and the satellite-ground link may have a Doppler shift greater than 600 kHz. Such rapid variation poses stringent challenges to the real-time tracking capability of receivers.

(2) Technical Challenges and Application Advantages

The large Doppler shift brings multiple serious challenges to Ka-band system design:

Conventional phase-locked loops (PLL) can hardly track large frequency offsets, requiring FFT-based frequency offset estimation and digital signal processing techniques.
Carrier interference (ICI) caused by large offsets is extremely severe, demanding dedicated anti-ICI algorithms.
Fast variation requires real-time update of compensation parameters, significantly increasing computational complexity.

Despite prominent technical challenges, Ka-band has outstanding advantages and is irreplaceable for high-rate LEO IoT applications:

Rich spectrum resources, with single-carrier bandwidth up to hundreds of MHz, supporting Gbps-level transmission to meet massive IoT data demands.
High frequency allows greatly reduced antenna size, facilitating miniaturized and low-power terminal design suitable for IoT devices.
Commonly used for inter-satellite laser links with single-link rate over 100 Gbps and BER as low as , supporting inter-satellite communication and enhancing overall constellation capacity.

III. Comparison of Doppler Shift Impacts in Other Major Bands

Besides L-band and Ka-band, S-band, Ku-band and K-band are also commonly used in LEO satellite IoT. Different frequency ranges lead to significant differences in Doppler shift magnitude, propagation characteristics and application scenarios, forming a complementary application pattern. A detailed comparison is shown below:

表格

Band	Frequency Range	Doppler Shift at 780 km	Main Advantages	Main Challenges
L-band	1.5–1.6 GHz	~38 kHz	Good propagation, mature technology, easy compensation	Scarce spectrum, limited expansion
S-band	2–4 GHz	~48 kHz	Good propagation, low cost, mature system	Crowded spectrum, limited high-rate capacity
Ku-band	12–18 GHz	~325.5 kHz	Moderate antenna, low rain attenuation, medium spectrum	Large shift, dedicated tracking required
K-band	18–26.5 GHz	~423.2 kHz	High spectrum efficiency, medium-high rate	Atmospheric absorption, heavy rain fade, large shift
Ka-band	26.5–40 GHz	480–600 kHz	Large bandwidth, small antenna, inter-satellite friendly	Extremely large shift, high complexity, strict hardware

Among them:

S-band achieves a good balance between performance and cost, mature and low-cost, widely used in satellite broadcasting and mobile communications.
Ku-band has moderate Doppler shift and antenna size, with much lower rain attenuation than Ka/K-band, widely applied in direct-broadcast TV and broadband access.
K-band features high spectrum efficiency for medium-high rate transmission but suffers from atmospheric absorption, rain fade and large shift, mainly used in high-speed data and radar applications.

IV. Divergent Requirements of Frequency Band Selection on Doppler Compensation Techniques

Doppler compensation is the core method to mitigate shift impacts and ensure communication quality. Due to large differences in Doppler magnitude, variation rate and signal properties among bands, the requirements on compensation techniques in terms of acquisition range, tracking bandwidth, algorithm complexity, hardware implementation and system integration also differ significantly.

(1) Different Requirements on Frequency Offset Acquisition Range

Acquisition range is a core indicator directly related to Doppler magnitude. Ka-band requires an ultra-large range above ±600 kHz, while L-band only needs about ±50 kHz.

L-band can use conventional PLL for low-cost acquisition.
Ka-band requires dedicated techniques such as FFT-based parallel estimation and large-offset search algorithms.

(2) Different Requirements on Tracking Bandwidth

Tracking bandwidth determines response speed to shift variation. High-frequency bands need wider bandwidth.

Ka-band (up to 0.27 ppm/s) requires millisecond-level response for real-time tracking.
L-band can use narrower bandwidth to improve noise immunity while ensuring accuracy.

(3) Different Requirements on Algorithm Complexity

High bands need more complex signal processing to tackle large shift, high variation rate and interference.

Ka-band suffers from severe inter-subcarrier frequency offset (ISFO), requiring dedicated ISFO compensation and joint time-frequency synchronization, greatly increasing computation.
L-band has minor ISFO and can adopt simplified algorithms to reduce complexity.

(4) Different Hardware Implementation Difficulty

Bands differ drastically in hardware performance requirements:

Ka-band needs high-speed ADC/DAC, wideband RF frontends and high-performance DSP, increasing cost and power consumption.
L-band uses conventional RF and processors, lowering terminal cost for large-scale IoT deployment.

(5) Different System Integration Complexity

Technical complexity directly determines integration difficulty:

L-band is mature with complete industry chain, low integration difficulty and fast large-scale application.
Ka-band has high complexity, strict professional requirements for design and testing, and slow promotion restricted by maturity.

הַבָּא: Analysis of Interference and Deviation of Doppler Shift on LEO Satellite IoT Positioning

בְּחֲזָרָה: Compensation Techniques and Comprehensive Countermeasures for Doppler Shift in LEO Satellite IoT Communications

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